The Google Books Ngram Viewer

The Ngram Viewer (https://books.google.com/ngrams/) can show you the frequency of certain (combinations of) words (over time). I often use the Ngram viewer when I correct student work to check collocations.

When you have two similar combination of words and you are not sure which one is the combination native speakers would use, you could enter both combinations in the search bar of the Ngram Viewer. Here is an example, which compares “is afraid of” with “is afraid by”:

The result shows clearly that “of” is preferred in this context.