题目

The Queen’s English is now sounding less upper-class, a scientific study of the Queen’s Christmas broadcasts has found. Researchers have studied each of her messages to the Commonwealth countries since 1952 to find out the change in her pronunciation from the noble Upper Received to the Standard Received. Jonathan Harrington, a professor at Germany’s University of Munich, wanted to discover whether accent changes recorded over the past half century would take place within one person. “As far as I know, there just is nobody else for whom there is this sort of broadcast records,” he sa用来判断镁在氧气中燃烧是化学变化的依据的是　 [     ]A．放出大量的热B．发出耀眼的白光C．镁条变短 　D．生成白色固体