秦朝短期而亡的主要原因是（ ）
A：匈奴的进攻
B：社会经济发展缓慢
C：秦朝的暴政
D：农民起义的打击
Mr White thinks that this picture is an art____（珍宝)．
-Your paintings are so great, David! When did you learn to paint?
-Three years ___________.
—Where is your father?
—He is __________ a trip to Hangzhou.
