题目

I’ve heard a whisper ________ David and Heather are heading for marriage.．   A．what          B．which         C．who           D．that 答案：D解析：考that引导的定语从句的用法。完成下列化学方程式：（1）电解水实验原理：                                                                    ；（2）铁丝在氧气中燃烧：                                                                ；（3）硫磺在氧气中燃烧：                                                                ；（4）铁钉与硫酸铜溶液的反应：                                                    ．