Look! There are some birds _______ in the sky. They are very beautiful.
A:to fly
B:fly
C:flying
D:flown
下列词语,从地质作用的观点看,正确的是( )
①水滴石穿 ②沧海桑田 ③稳如泰山 ④三十年河东、三十年河西 ⑤坚如磐石