题目

阅读下面材料，在空白处填入适当的内容或括号内单词的正确形式。On keeping a Diary in EnglishKeeping a diary in English is one of the【1】(effect) ways to improve our English writing ability.【2】(compare) with other forms of writing, it is shorter and takes【3】time. It can help us to develop the habit of thinking in English.【4】we persist in this practice, gradually we’ll learn how to express ourselves in English. In keeping a diary in English, we certainly run up against many【5】(difficult). In the first place,【6】often happens that we have trouble如图，放在水平面上的物体受到水平向右的力F1=7N和水平向左的力F2=2N的共同作用，物体处于静止，那么A. 如果撤去力F1，那么物体受到的合力为2NB. 如果撤去力F1，那么物体受到的合力为零 .C. 如果撤去力F2，那么物体受到的合力一定为2ND. 如果撤去力F2，那么物体受到的摩擦力一宠为7N