他在试卷上写下了x5代表第五题。

He wrote ___x5 on the test paper to represent question five.

我更喜欢x5型号的设计，它更符合我的需求。

I prefer the design of the ___x5 model as it better suits my needs.

这道题要求计算4x的5次方等于多少。

This problem asks you to calculate what 4___x^5 equals.