I'm Amy Black．I have never seen sharks in the____．But as a(n)____，I have seen sharks in an aquarium(水族馆)．

    ____，there are between 200and 250 kinds of sharks of different sizes．Sharks are much____than other fishes．The largest carl be as long as 15____ largest shark____about 3，200 kilos．Usually sharks don't attack(攻击)people．Sometimes they attack people____themselves．One of____sharks is the Great White Shark．They attacked a lot of people on the beaches of America．

I'm waiting for my friend. _______, I'll go shopping alone.

从标有-5a²b , 2a²b² , $\frac{2}{3}$ab²  ,  -5ab的四张同样大小的卡片中，任意抽出两张，“抽出的两张是同类项”这一事件是（     ）