氨甲蝶呤可用于治疗白血病的原因是其可以直接

A．抑制二氢叶酸还原酶

B．抑制DNA的合成酶系的活性

C．抑制蛋白质的分解代谢

D．阻断蛋白质的合成代谢

E．破坏DNA的分子结构

The nurse is teaching breast self-examination (BSE) to a college student. The nurse knows that the client understands the best time to examine her breasts when she says:（）.

A．"I'll examine my breasts 1 week after my period starts. "

B．"I'll perform a BSE just before my period starts. "

C．"I must examine my breasts the same time each day. "

D．"Every time I shower I'll do a breast examination. "