— Is Jack on duty today?

— It ________ be him. It's his turn tomorrow.

A．mustn't

B．won't

C．can't

D．needn't

白助烟身份与内在质量有一定的关系．表现在（）

A.中下部叶以稍薄质量较好．适中和稍厚香气较差

B.上部红黄色烟叶以稍薄叶香味质量较好．适中、稍厚叶香味质量较差

C.上部红棕色的烟叶以稍薄至适中烟叶质量稍好，稍薄叶余味稍苦，有杂气．内在质量稍差

D.白肋烟以过薄或过厚质量较好