计算-（-3a） 的结果是（    ）

“春运”被誉为人类历史上规模最大的人口大迁徙。“春运”期间，中国大陆交通承受了巨大压力。2011年初，某地出台了“春运”措施，并举行“我为‘春运’献计”活动。作为公民，你认为下列参与方式恰当的有(     )
①投票表达自己对“春运”措施的态度，行使表决权
②向有关部门提出意见，通过社情民意反映制度参与民主决策
③对“春运”措施的不完善、不合理之处提出批评、建议，行使监督权
④要求召开居民会议，讨论“春运”事宜，参与民主管理

阅读下面短文,从方框内选择恰当的句子填入短文空白处,使短文内容完整、意思连贯。
____  He is in Grade Seven this year. He likes reading news and watching football games.____  He does his best to know where and when there is a football game in the newspapers.
Now Peter is having lunch.____  He is very happy because there is a nice football game on TV at four this afternoon.____  But he has to have English and Chinese classes. He thinks and finds a way.
“Hello, Mrs. Black!” Peter says to his teacher on the telephone, “Peter is ill(生病) in bed. He wants to ask for half a day’s leave(请半天假).”
“Oh,____  ” says Mrs. Black, “But who's that?”
“It’s my father, Mrs. Black.”

A. I'm sorry to hear that. B. He is listening to the radio（收音机）, too. C. Peter is thirteen years old. D. He wants to watch it very much. E. And he likes reading newspapers.

新文化运动由前期宣传民主与科学转变到后期宣传马克思主义，其主要原因是（   ）

在 探究“质量一定时物体的加速度与力之间的关系”实验中：

①某次实验打出了一条纸带如图所示。从比较清晰的点起，每5个点取一个计数点，量出相邻计数点之间的距离（单位cm）。该次实验小车的加速度a＝____ m/s²。(结果保留两位有效数字)

②以合外力F为横轴，以加速度a为纵轴，根据测得数据画出a-F图线，发现图象是一条过原点的直线，由此得到的实验结论是____。