题目

—I didn’t hear you come in just now.    — That’s good. We tried ____any noise, for you were sleeping.     A. not make         B. not to make          C. to make          D. making 答案：B据英国《自然》杂志报道，科学家最近研制成了以锶原子做钟摆的“光格钟”，成了世界上取精确的钟．已知一种锶原子的相对原子质量为88，其质子数是38，则这种锶原子的核外电子数为（ ）A．38B．50C．88D．126