请教pp中5道语法题目，非常感谢

1. A common way to produce x-rays is (      ) electrons into a copper target.

a. Fires    b. fired    c. by firing    d. how to fire

我不知道答案是什么，只觉得都不对。无奈下选了d，还是错。

2. Education in the United States is overseen by (local) school districts, (which) follow (regulations) mandated by their state (government).

我不知道答案是什么。

3. Photographer Edward Steichen constantly (experimented new) techniques and materials (in) his quest (to have) photography accepted (as) a creative art.

答案是a，我猜对了

4. Working (by) chemical reaction, and being (independence) of atmospheric oxygen, rockets are used (to power) interplanetary (space) vehicles.

答案是b，我选了a

5. The Mississippi riverboat, which (evolved) from simpler (steamship) of the early 1800’s, became the (dominant) form of (passenger transport) on the Mississippi River.

答案是b, 我选了d

请您指教，非常谢谢。

谢谢。我下载了，但是不能用。现在我已经明白了1和4，能否帮我简单讲解一下其他3个。还有几天就要考试了。

非常感谢。

非常谢谢。

这个解释也非常合理，我能够接受。

谢谢你sofarsgood。祝你好运。