单选题 The children ______ very quiet; I wonder what they ______ up to.
  • A. were; are being
  • B. are being; are
  • C. are; do
  • D. are being; do


【正确答案】 B
【答案解析】be用于进行时可表示一个暂时的特点或表现。What they are up to相当于What they are doing。