题目

 His children are well-behaved, while ________ of his sister are rude. A. the one                       B. that                              C. those                      D. ones 答案：C4．设a，b∈R，则“a＞1，且b＞1”是“a+b＞2”的（　　）A．充分不必要条件B．必要不充分条件C．充分必要条件D．既不充分又不必要条件