① ____ A. This is cow.
② ____ B. The pig goes “oink, oink” .
③ ____ C. What’s that? It’s a chick.
④ ____ D. Eat a cake.
“木桶效应是指组成木桶的木板如果长短不齐,那么这只木桶的盛水量,不取决于最长的那一块木板,而是取决于最短的那一块”,下列决策有助于提高一个地区环境人口容量的是( )