动词填空， 用括号内所给动词的适当形式填空。
1. Xiao Li promised to chat with me on the Internet, but so far he __________ (not do) so.
2. At the moment we have too much to do __________ (think) of doing anything else.
3. Last Friday afternoon the young man __________ (hurt) in the traffic accident which happened
on the highway.
4. Sound __________ (travel) through air at a speed of about 340 metres per second.
5. Food cannot __________ (keep) properly in a fridge at an unsuitable temperature.
6. The snow __________ (stop) when she woke up and the sun was shining brightly.
7. Every one of us was excited, for in a few minutes we __________ (see) Liu Xiang appear on the
sports ground.
8. The Women's World Cup __________ (not begin) until 1991 when China hosted it in Guangzhou.
9. Understanding yourself is very important to __________ (build) self-confidence.
10. On Earth, gravity keeps our feet on the ground and makes anything we drop __________ (fall) towards
the ground.
2SO3(g)；ΔH＝－197．74 kJ·mol－1。