With practice people can learn to change their social habits.
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注射模的排气方式有( )和( )。排气槽通常开设在型腔( )部位。最好开在( )上,并在( )一侧,这样即使在排气槽内产生飞边,也容易随塑件脱出。
Z1-03-18 质点作直线运动,位置矢量的方向一定不变。
A. 对
B. 错
Z1-03-22物体具有恒定的加速度,必作匀加速直线运动.
A. 对
B. 错
The author’s purpose in writing this passage is to explain .
A. why it is necessary for us to help others
B. how to help others
C. who most need help
D. what community service is