退火指金属材料加热到适当的温度，保持一定的时间，然后（）冷却的热处理工艺。
参考答案：缓慢
—Did your father phone you shortly after the accident?
—No, it was a fortnight ________ he gave me a phone call.
A．since
B．when
C．while
D．before
简述DHTML的概念及主要组成。
