this these those的用法和区别

例句：

This knife needs sharpening.

这把刀需要磨了。

This material frays easily.

这布料容易磨损。

Those laws no longer pertain.

那些法律已不适用了。

These questions frustrated me.

这些问题使我懊丧。

These injuries were avoidable.

这些伤病本是可以避免的。