____，____。但为君故，沉吟至今。（《短歌行》）

下列公式中，既适用于点电荷产生的静电场，也适用于匀强电场的有(     )
①场强$E=\frac{F}{q}$; ②场强$E=\frac{U}{d}$ ③场强$E=k\frac{Q}{r^2}$     ④电场力做功$W=qU$

恩格斯说“这是一次人类从来没有经历过的最伟大的进步的改革，是一个需要巨人——在思维能力、热情和性格方面，在多才多艺和学识渊博方面的巨人时代。”这个巨人时代指的是（   ）

小玉根据电路中的小灯泡是否发光判断电路中有无电流，采用的物理学研究方法是（　　）

阅读下面材料，在空白处填入适当的内容（1个单词）或括号内单词的正确形式。

     The giant panda ____(love) by people throughout the world. Chinese scientists ____(recent) had a chance to study a wild female panda with a newborn baby. She was a very ____(care)mother. For 25days, she never left her baby, not even to find something ____(eat)! She would not let any other pandas come near. She licked the baby constantly to keep it clean. Any smell might attract natural ____(enemy) that would try to eat the little comforting pats. The mother held the baby in herfront paws much the way a human does. ____ it cried, she rocked it back and forth and gave it little comforting pats, The mother continued to care for the young panda ____more than two years. By that time, the panda no longer needed ____(it) mother for food. However, it stayed with her and leaned about the ways of the forest.Then, after two and a half years, the mother ____(drive)the young panda away. It was time for her to have a new baby, ____itwas also time for the young panda to be independent.