—Jack, you look very tired today.

—Yes, actually I've been _____ busy these days _____ I can't get enough sleep. [ ]

A. so, that

B. such, that

C. too; to

D. such a; that

为了能使切割顺利进行，被切割金属燃料的燃点应（）熔点。

A.低于

B.高于

C.较低于

D.等于