题目

Old McDonald gave up smoking for a while, but soon ______to his old ways. A. returned                  B. returns         C. were returning D. has returned 答案：A有关生物圈的叙述，最准确的一种是 （ ）A. 大气圈的底层 B. 全部水圈 C. 岩石圈上部 D. 地面以上10千米到水下10千米的薄层