两个动名词并列作主语,谓语是否用单三,为什么?

这要分情况而言：
由and连接的两个(或多个)动名词或不定式作主语,如果并列的动名词或不定式语义相同或相似,谓语用单数；如果语义不一致,则谓语用复数.例如：
Lying and stealing are not right.
To love and to be loved is sweet to me.
Weeping and wailing does nothing towards solving the problem.
Reading Ibsen and solving maths problems are different assignments