形成我国成灾人口与农业灾情严重的原因主要有( )①国土面积广大;②人口众多;③悠久的农业历史状况;④自然灾害种类多样,灾次频发
A:①②③
B:②③④
C:①②④
D:①③④
_____ all the inventions have in common is ______ they have succeeded.