风湿性心脏瓣膜病中，哪一项最易引起心绞痛
A．主动脉瓣狭窄B．主动脉瓣关闭不全C．二尖瓣狭窄D．二尖瓣关闭不全
参考答案：A
According to the first paragraph, which of the following is true
A．People don't have to gain education.
B．People don't have to learn job skills.
C．People don't have to be treated as equals.
D．People don't have chances to begin anew.
A．图象中的DE段是冰的熔化过程
B．AB、CD段物质在吸热，BC、DE段物质没有吸热
C．水的凝固点是O℃
D．BC段物质的温度保持不变，内能不变
