Today we tell you about some new understanding of why cutting the main branch of a plant
or tree can lead to better development.
     The findings are from researchers on two_continents.Professor Prezemyslaw Prusinkiewicz
of the University of Calgary in Canada led the research with scientists from Britain and Sweden.
Their study appears in the Proceedings of the National Academy of Sciences.
     Researchers have known since the 1930s that the actively growing tip of a plant produces
a hormone(荷尔蒙)called auxin(生长素)．This hormone flows down the main stem.Scientists
say the auxin has an indirect effect on buds(芽)on the side of the stem to prevent branching.
T     hese buds themselves also produce auxin.The research suggests that to grow,they have
to be able to export the hormone into the main stem.But the flow from the stem tip prevents
them from doing this.The researchers wanted to find out how this blocking happens.
     Professor Prusinkiewicz is on leave in Australia,but he sent us an e－mail suggesting a
simple way to understand the process.Think of a major road crowded with traffic.So many
cars are on the main road that the cars on the side roads cannot enter.
     The stem is like the crowded main road.The new research shows that the buds on the
side cannot export their auxin into the main stem because it is too full.But if that main shoot
is pruned(修剪),other buds below it can start exporting.They are no longer prevented from
growing.
     Ottoline Leyser from the University of York says that after a plant is pruned,all the
inhibited(被抑制的)shoot tips compete with each other to grow.In doing this,the branches
influence each other's growth.Nearby shoot tips are more likely to affect each other than those
that are far apart from each other.
     Professor Leyser says the strongest branches grow best,wherever they may be on the
plant.The study found that the main shoot grows the best of all not because of its position at
the top of the plant,but mostly because it got there first.

A．Researchers have recently found out that the growing tip of a plant produces hormones.
B．Auxin has a direct effect on buds to keep branches from growing.
C．Buds on the side of the stem can’t produce hormones.
D．In order to grow，the buds on the side of the stem export the hormones into the main stem.

A．take the problem seriously if their daily life is disturbed
B．discuss the seriousness of the problem with their children
C．take their children to see the doctor immediately
D．keep their children away from their rebellious friends

     A major source of teen stress is school exams,and test anxiety is not uncommon.When
you recognize your teen is under stress,how can parents help your teen stay calm before
an exam?
     Be involved.Parents need to be involved in their teen's work.__1__What they look for is
your presence-to talk,to cry,or simply to sit with them quietly.Communicate openly with your
teen.Encourage your teen to express his worries and fears,but don't let them focus on those
fears.
     Help them get organized.__2__Together,you and your teen can work out a timetable in
which she can study for what she knows will be on the test.
     Provide a calm setting.Help your teen set up a quiet place to study and protect his privacy.
Give them a nutritious diet.It's important for your teen to eat a healthy,balanced diet during
exam times to focus and do her best.__3__If this happens,encourage your teen to eat light
meals or sandwiches.A healthy diet,rather than junk food,is best for reducing stress.
     __4__Persuade your teenager to get some sleep and/or do something active when she
needs a real break from studying.Making time for relaxation,fun,and exercise are all important
in reducing stress.Help your teen balance her time so that she will feel comfortable taking time
out from studying to spend time with friends or rest.
     Show a positive attitude.__5__Your panic,anxiety and blame contribute to your teen's
pressure.Make your teen feel accepted and valued for her efforts.Most importantly,reassure
your teen that things will be all right,no matter what the results are.

A．A parent's attitude will dictate their teen's emotions.
B．Exam stress can make some teens lose their appetite.
C．They will only make the situation worse.
D．Encourage your teen to relax.
E．The best thing is simply to listen.
F．Help your teen think about what she has to study and plan accordingly.
G．Your teen may also make negative comments about themselves.