A.a chemical compound  
B.The tip of a root
C.A biochemical process  
D.A type of plant cell

A.The results of two experiments are compared
B.A generalization is made and several examples of it are given
C.A hypothesis is presented, and several means of providing it are suggested
D.The findings of an experiment are explained

A.The relationship between a plant’s roots and its shoots
B.How plants can be grown without roots
C.What can be learned by growing roots in isolation
D.What elements are necessary for the growth of isolation

A.obtain organic compounds from the roots
B.do not require water
C.have begun photosynthesizing
D.“export” protein in the form of amino acids

A.necessary
B.predictable  
C.useful  
D.successful

A.highly-paid
B.unemployed  
C.busy  
D.employed

A.highly-paid
B.unemployed  
C.busy  
D.employed

A.Vietnam exports a lot of rice which grown mainly in the south of the country.
B.Vietnam exports a lot of rice, that is mainly grown in the south of the country.
C.Vietnam, which is grown mainly in the south of the country, exports a lot of rice.
D.Vietnam exports a lot of rice grown mainly in the south of the country.

A.The fire is thought to have been started on purpose.
B.They think that the fire which was started by someone on purpose.
C.The fire is thought to be started on purpose.
D.Someone is thought to start the fire on purpose.

A.The fire is thought to have been started on purpose.
B.They think that the fire which was started by someone on purpose.
C.The fire is thought to be started on purpose.
D.Someone is thought to start the fire on purpose.