华北平原发展农业的制约因素是( )
A:地形崎岖
B:水资源缺乏
C:光热资源不足
D:劳动力不足
① ____ A. birthday B. we C. she
②____ A. nine B.blow C. eight
— Let's go to Huangyao Old Town next weekend, shall we?—Sorry. I ____there many times. I don't want to go again.
有关宇宙和天体的说法,正确的是( )