----You park here! Look at the sign, it says “No parking”.
----Sorry, I didn't notice that sign just now.
A:won't
B:needn't
C:mustn't
D:couldn't
种子萌发的外界条件是:种子萌发时需要适量的____、适宜的____和____的空气.
如果DNA分子上某一片段是基因,则该片段 ①携带遗传信息 ②上面有密码子 ③能转录产生mRNA ④能进入核糖体 ⑤能运载氨基酸 ⑥能控制蛋白质的合成
将含盐15%的盐水30千克,蒸发成含盐90%的食盐颗粒,需要蒸发掉多少千克的水?