In my view, biology is ________ chemistry, but a little easier than mathematics．

a subject so difficult as

as difficult a subject as

as a difficult subject as

difficult as a subject as

As a boy of six, ________．

Tim's parents asked him to play the piano every day．

Tim and his parents would play the piano together．

Tim had to practice playing the piano every day．

to learn playing the piano is too hard for Tim．

Tired of the noise, ________．

he shut the door

the door had been shut

he had shut the door

the door was shut

________ get such a nice necklace?

Where do you think can I

Where do you think I can

Do you think where can I

Do you think where I can

Only after my friend came ________．

did the computer repair

he repaired the computer

was the computer repaired

the computer was repaired

I don't think the park ________．I prefer to go to a theme park．

is worth being visited

is worthy being visited

is worthy to visited

is worth a visit

So involved with computers ________ that the leaders at the summer computer camps often had to force them to break for sports．

has the children become

did the children become

has become the children

became the children

When changing lanes, a driver should use his turning signal to let other drivers know ________．

he is entering what lane

which lane he is entering

he is entering which lane

which lane is he entering

Only under special circumstances ________ to take those tests．

are freshmen permitted

freshmen are permitted

permitted are freshmen

are permitted freshmen

The problem is ________．

worth paying attention

worthy to be paid attention

worthy being paid attention

worthy of being paid attention to