You’d better find a pen pal if you don’t get much writing (write) practice .为什么填writing

You’d better find a pen pal if you don’t get much writing (write) practice .为什么填writing

writing在此处是动名词作定语,有特定的含义：写作.
如果你想做大量的写作练习,你最好交个笔友.

writing 作practice 的定语。写作训练