. –Hi, Mary. Would you like to go to the concert this evening?

--Sorry, Tom.         Tomorrow’s lessons, I have no time to go out with you.

A．Not preparing

B．Not having prepared

C．Not to prepare

D．Being not prepared

下列有关固定化酵母细胞制备步骤不恰当的是 [ ]

A．应使干酵母与水混合并搅拌，以利于酵母菌活化

B．配制海藻酸钠溶液时要用小火或间断加热方法

C．向刚溶化好的海藻酸钠溶液加入已活化的酵母细胞，充分搅拌并混合均匀

D．将与酵母混匀的海藻酸钠液注入CaCl₂溶液中，会观察到CaCl₂溶液有凝胶珠形成