活动材料是指能更好地使课堂教学目标内化为学生素质的物质化材料，如实物、标本、投影、模

As I was sitting down for dinner,the telephone ________ring.

A．should

B．must

C．could

D．would

脂肪酸合成的原料乙酰CoA从线粒体转移至胞液的途径是

A．三羧酸循环

B．乳酸循环

C．糖醛酸循环

D．柠檬酸-丙酮酸循环

E．丙氨酸-葡萄糖循环

旅行社应当妥善保存《旅行社条例》规定的招徕、组织、接待旅游者的各类合同及相关文件、资料，保存期应当不少于（）

Of all the students, Mary is the (early) __________ to come to school.