A：把打点计时器固定到铁架台上，并用导线把它和低压直流电源连接起来
B：把纸带的一端固定到重物上，另一端穿过打点计时器的限位孔，把重物提升到一定高度
C：接通电源，释放纸带
D：用停表测出重物下落的时间
下列各句中划线的词语，使用恰当的一句是（ ）
孙中山在黄埔军校开学典礼上说：“……一生一世，都不存升官发财的心理，只知道做救国救民的事业。”两年后，该校师生积极投身的“救国救民的事业”是（ ）
⑴Mom and Dad are the most important people in your life. They have been looking after you since you were born. ⑵你应该一直爱他们。You should also get on well with them. But some children don't know how to do this. Here are some ways to help you. Spend more time with your parents. ⑶Don't spend too much time playing computer games or watching TV. Ask your parents to play with you. ⑷和他们交谈或者散步。 Be kind to your parents. You can make them happy with a smile when you come home. You can send your mother a card on Mother's Day or tell your father a joke on his birthday. ⑸You can also clean your room by yourself. Work hard. If you do your best in your studies, your parents will be proud of you.
