甘肃省的农业区主要分布在( )
A.河西走廊
B.河套平原
C.藏南谷地
D.湟水谷地
答案:A
取鸡蛋1枚,把它的钝端埋在盛有黄砂的烧杯内(约埋入1/2),把烧杯放在垫有石棉网的三脚架上,用酒精灯加热.待黄砂加热后,在蛋壳上会出现点点小水珠,这证明蛋壳上有许多______,其作用是______.
The ice isn't _____ to skate on.[ ]
A. thin enough
B. enough thin
C. thick enough
D. enough thick