在一个不透明的箱子里放有x个除颜色外其它完全相同的球，这x个球中白球只有3个，每次将球搅拌均匀后，任意摸出一个球记下颜色再放回箱子，通过大量重复摸球实验后发现，摸到白球的频率稳定在30%，那么可以推算出x最有可能是____ 个．

连线。

①Can your father play football? ____                             A. Yes, she can.

②Can she ride a bike? ____                                           B. Here you are.

③Here's a card for you. Happy Teachers' Day! ____       C. No, he can't.

④Give me a balloon, please. ____                                   D. Thank you.

下列所使用的试剂必需现配现用的是
①斐林试剂     ②二苯胺试剂      ③双缩脲试剂      ④龙胆紫