The lecturer's humour was ---make every attendant burst into

应该是such as to.
本题主要考察A和B的区别,C和D比较容易排除
A和B的区别如下：
so as to:
为的是,以便
例句与用法:
1.He ran quickly so as to catch the last bus.
他跑得很快以便赶上那末班车.
2.The two lovers dropped back so as to be alone.
那对情人落在后面,为的是两人好单独在一起.
such as to:
达到这样的程度以致
例句与用法:
1.His speech is such as to incur enmity.
他的演说会引起别人的敌意.
2.Her madness is not such as to fill her mother with despair.
她还没有疯到令其母亲绝望的程度.