A:①②③
B:①②④
C:①③④
D:②③④
关于地形与城市区位关系的叙述,正确的是( )
—How long ________they_________?—Sorry, I don't know. But I know that Mr. Chen is going to _______a nurse next month.
下列几项中对变异在生物学和实践上有重要意义的说法不正确的是( )