Sue forgot to bring her textbook,so she asked if she could -

选择D.
句子意思：Sue 忘记带她的课本了,所以问她可否借一下她同学的书.
选择D 是因为短句 if she could xxx her classmate's book 是虚拟语气,此时Could + 动词原形表示虚拟语气.
lend 意思是借给 主语借出东西给别人.如：I lend some money to Penny.我借了钱给penny.
borrow 是借 主语向别人借东西.如：I borrowed some money from Penny. 我跟penny借了点钱.