单选题 ______any trouble with the boiler, the automatic controlling unit will cut off the fuel oil supply.
A．There should be B．If there had been
C．Should there be D．If there was

【正确答案】 C

【答案解析】[解析] 30．此句为倒装形式的虚拟条件句，相当于If there should be any trouble with the boiler, 与将来可能情况相反。