There _______some writing paper on my desk. A is B are C am D were

选A。
paper 不可数
some 既可以修饰可数名词复数，又可以修饰不可数名词

A
paper是不可数名词，动词用单数

A is paper 纸张是不可数名词 所以用is

There __A____some writing paper on my desk. A is B are C am D were