曝气池供氧的目的主要是供给微生物分解（）所需的氧。
参考答案：有机物
根据图中小磁针的指向以笔代替导线，画出螺线管上导线的绕法．
—Do you _____ a ping-pong ball?
—Yes, I do. And my brother _____ a soccer ball. [ ]
A. has, has
B. have, has
C. have, have
D. has, have
