On the evening of October 7, Li Feng was watching TV while his mother was ____ b      cooking supper in the kitchen. ____ S       the telephone rang. Li Feng ____ q     picked it up to____ a        the call. It was from a good friend of his____ m     . She wanted to say “Happy Birthday” to his mother. "Today is Mother's birthday, but I have already____       f_____all about it. Mother gives me a lot of____ l      and care while I didn't care for her____ e    . From now on, I must always____ r     this, ____ s     my love to her and care for her enough,” Li Feng thought to himself, feeling a little ashamed(惭愧的).

①受多种因素的制约，财政收支完全相等的情况几乎不存在

②只有财政盈余才有利于促进国家经济发展

③收入大干支出略有盈余，或支出大于收入略有赤字，都属于财政收支平衡

④财政赤字不利于促进国家经济发展

如图所示，一个挂在绝缘细线下端的带正电的小球B，静止在图示位置，若固定的带正电的小球A的电荷量为Q，B球的质量为m，带电荷量为q，θ=30°，A和B在同一条水平线上，整个装置处于真空中．求：