A:to laugh at
B:to laugh
C:being laughed
D:being laughed at
下图是转基因抗冻番茄培育过程的示意图(ampr为抗氨苄青霉素基因),其中①、④表示相关的操作步骤,甲、乙表示相关结构或细胞。Pst I酶和Sma I酶切割基因后将产生同的粘性末端。据图分析下列说法错误的是
﹣2的倒数是( )
计算:274×(13-1)÷(﹣3)2
— What did he _______ just now?— Sorry, I didn't catch his words. I_______ about something else.