So the weather satellites are _of_ great help to the scientistsat the station,in the past they could forecast the weather for about 24 or 28 hours earlier.为什么是of?

问题描述:

So the weather satellites are _of_ great help to the scientists
at the station,in the past they could forecast the weather for about 24 or 28 hours earlier.
为什么是of?

of great help =helpful
记住类似的这种用法.