—Tom didn’t come last night,did he?

—No.I _______ have waited for him.A whole night was wasted.

A．would

B．should

C．couldn’t

D．needn’t

生产微生物油脂时，培养基中C/N对油脂的积累影响较大，一般情况下培养基中含氮量越高，则细胞中蛋白质含量越高，而且碳含量越高，油脂积累量越高；