it用法？

例句：

It doesn't have the market to itself.

它未能独占市场。

She lost it, just as I said she would.

我就说了吧，她把它丢了。

It was a time of peak demand for the product.

那是对该产品需求最旺的时期。

It is less of a problem than I'd expected.

问题不像我预料的那么大。

It is estimated the project will last four years.

据估计，这项工程将持续四年。