A:充分利用杂种优势
B:保护环境中物种的多样性、维护生态平衡
C:保护自身知识产权
D:避免出现新基因
如图1,我们把对角线互相垂直的四边形叫做垂美四边形.
—Would you mind picking up the last cigarette on the playground?
—_______. I'll do it right away.