题目

C        At present, in many American cities expecially, many teachers in the public schools say they are underpaid. They point to jobs such as secretary or truck driver, which often pay more to start than that of a teacher. In many other fields, such as law, medicine, computer science, a beginning worker may make more than a teacher who has taught for several years.        Teaching has never been a profession that attracted people interested in high salaries. It is by history a profession that has provided rewards in addition to money—the satisfaction of sharing knowledge, of in氢元素和氧元素的本质区别在于（ ）A.相对原子质量不同B.核电荷数不同C.元素符号不同D.核外电子数不同