自然界的铁矿石大多以共生矿物形式存在。
参考答案:对
---On summer nights the weather is usually very hot.
---Yes, so I often go to sleep ______ the windows ______.
A.with, on
B.have, open
C.with, open
D.with, closed
主动脉瓣狭窄致猝死的常见原因()。
A.心排血量不足致脑供血不足
B.急性心肌缺血致心室纤颤
C.在主动脉瓣口面积1cm左右时出现
D.急性左心衰竭
E.急性心肌缺血致心肌梗死