None of us is deserving of full credit .此句中为什么要用“is”,请问.

is 和 are其实都可以的.
以None of 开头的句子,谓语动词用单数或复数均可.
None of.作主语,强调个体时,谓语动词用单数；
若强调整体时,谓语动词则用复数.
例如：None of them has a bike.他们当中没有一个有自行车的.None of them have bikes.他们全都没有自行车.