-Is（ )important for student have healthy habit?A.it B.that 选啥?

楼主,你的题目有点小错,student需要加s,have前需加to.
-Is（ it )important for student to have healthy habit?
解析：It is adj to do..做...很...,it 是形式主语,is adj 是系动词,to do 后面的是真正的主语.这里不过是采用疑问句罢了.另外,只有it可以做形式主语,故选A.
祝开心~!