瘀血痹阻型胸痹心痛的特点是
A．心胸隐痛，痛无定处B．心痛如刺，痛有定处C．心胸绞痛，心痛彻背D．心胸灼痛，时作时止
参考答案：B
___ is the most useful invention?
A．Do you think which of these
B．Which of these you know
C．Which of these do you know
D．You know which of these
春天是放风筝的好季节．风筝在空气中飞行利用了下列什么原理（ ）
A．风筝下方空气流动速度小，空气压强小
B．风筝下方空气流动速度大，空气压强大
C．风筝上方空气流动速度大，空气压强小
D．风筝上方空气流动速度小，空气压强大
