有一读者问： 有这样一道选择题：
(1)One of the requirements for a fire is that the material_________to its burning temperature.
A. were heated B.must be heated
C. is heated D.be heated
我选的B，而答案是D，请问我错在哪里？
这里须选用be heated （=should be heated），因为这种由that引导的表语从句的谓语须是“虚拟式（should)+动词原形(should亦可不用）”。上述句型的主语常常是表要求或建议的名词如requirement, suggestion, proposal, request等，再如：
(2)My suggestion is that we （should）tell him.
(3)Our request is that he （should）be left alone.
