液压泵站额定压力不得低于（），乳化液浓度应达到3～5%。
参考答案：30Mpa
The last time we had great fun was _____ we were visiting the Water Park.
A．where
B．how
C．when
D．why
钟表8时30分时，时针与分针所成的角的度数为（ ）
A．30°
B．60°
C．75°
D．90°
