By the time the fire engines arrived,the house__to the ground.a was burnedb has been burnedc had been burnedd should have been burnedby the time是用于对将来的假设还是什么呢?

Question

By the time the fire engines arrived,the house__to the ground.
a was burned
b has been burned
c had been burned
d should have been burned
by the time是用于对将来的假设还是什么呢?

Answer 1

C by the time 是完成时的标志,即：从句出现by the time,主句要用完成时态.此题的从句是过去时态,所以主句使用过去完成时,若从句是现在时态,则主句用现在完成时.意思是：等到救火车到达的时候,房子早已烧尽了.