机枪每秒钟射出15颗子弹．每颗子弹质量为0.02kg，射出的速率为800m/s，则射击时的平均反冲力大小为（）

The_(month)salaryforthepositionwillbenegotiableataround$2,000.

弹簧振子沿水平面做简谐振动，总熊量为E，若其振幅增加为原来的两倍，则总能量变为（）

Hismotherbecomesdisappointedwheneverhefailstoliveuptoher________(expect)

Thisadvertisementisa___(type)exampleoftheirmarketingstrategy.