________ is known to all is that effective measures should be taken to deal with the problem of the over­exploitation of our resources.

A．What

B．It

C．As

D．Which

(91～93题共用题干)
男性，65岁。2个月来反复发作胸骨后疼痛，发作与劳累关系不大，常在半夜或凌晨5时发作。

该患者最可能的诊断是

A．稳定型心绞痛

B．变异型心绞痛

C．初发劳力型心绞痛

D．急性心肌梗死早期