11. What(invention) do you think is the most important for people? 12. Christmas is a wonderful festival,(especially) for children. 13. I don't know when it began (to rain) last night. 14. The boy has at(least) twenty toys. 15.It was a very (powerful) country many years ago.第13题要注意,主语是人的时候,可以begin to do和begin d...