John was not listening and made a _____ answer when called upon to recite. [ ]

A. tough

B. dull

C. delicate

D. random

DNA是由什么组成（）

A.脱氧核糖核苷

B.脱氧核糖核酸

C.核糖核酸

D.脱氧核糖核苷酸

E.核糖核苷酸