in their opinion 中的 opinion有复数么?

in their opinion 中的 opinion有复数么? 为什么in their opinion中的opinion不加s? in their opinion还是 in their opinions? in their opinion opinion后是否加s "in my opinion"中的opinion可以加s吗 in one's opinion中的opinion加不加s opinion 是in their opinion还是in their opnions unqualified audit opinion 有qualified audit opinion么? In my opinion,the students had better finish their college In my opinion,their friendship has survived the passage time people is limited for expression their opinion in some count