你有个答案打重复了吧
正确答案选make understood
make understand 也可以不过不是在这种情况下
而是
She couldn't make her students understand her words.
这是主动的
而你原句
She couldn't make her words understood by her students.
被动语态...
只有选make understood.
get understood意思为,弄懂...
如果用get该写为
She couldn't get her students to understand her words.