Question

Mom，I'm afraid it's going to rain．The clouds in the sky are ________．

1. A.
   building up
2. B.
   breaking up
3. C.
   staying up
4. D.
   getting up

Answer 1

A
句意：妈妈，恐怕要下雨了。天空中的云越来越密集了。build up逐渐增加，符合句意。break up打碎，分裂，解体；stay up不睡觉，熬夜；get up起床。