The zoo keeper is worried because the number of visitors smaller and smaller .A. is becom

问题补充：

The zoo keeper is worried because the number of visitors smaller and smaller .

A. is becoming

B. become

C. became

D. to become

答案：

(答案→)A. is becoming

B. become

C. became

D. to become

解析：动物园饲养员很担心，因为游客的数量越来越少。结合语境可知下文为原因状语从句，描述的是现在正在进行的动作，故用现在进行时态，选A。