Some students become worried because they_____study very hard and get high grades.
问题描述：
Some students become worried because they_____study very hard and get high grades.
A can B may Cshould Dhave to
为什么是C而不是D,说下理由,帮我区别一下它们两个!
答
D是不得不是外在因素的迫使因为要很用心学习然后拿高分,所以他们很忧虑
C是应该没有 have to 强烈