问题补充：
One of the requirements for a fire is that the material to its burning temperature.
A. is heated
B. be heated
C. would be heated
D. shall be heated
答案：
A. is heated
(答案→)B. be heated
C. would be heated
D. shall be heated
解析：句意：对火的要求之一是材料要被加热到燃点。主语是requirement，suggestion，order，advice等词后面的表语从句中用虚拟语气：should do，should可以省略，而且material和heat是被动关系，用被动语态，选B。
