16.　 These put the ___________(矿物质) back into the soil, making it rich and healthy.

15.　 It refers to crops growing with natural rather than chemical ____________ .(肥料)

14.　 A ___________ (化学的) change takes place in paper when it burns.

13.　 This book is intended for students of advanced __________ .(水平)

12.　 America _______________ (出口) a large quantity of products to Africa and Southeast Asia.

11.　 The explorers ____________(装备) themselves with everything they needed and set off.

10.　 Lots of grain is attacked by __________. (害虫)

9.　　　 They ___________ (使迷惑) me with so many questions.

8.　　　 My teacher asked me to write a _________________ (摘要) of this report.

7.　　　 I am not all ________________ (满意) with the present situation.