A. Keep searches specific and avoid wildcards where possible.

Specific searches yield more relevant results and perform better. While wildcards (*) can be useful for broad matching, they can also significantly increase the search scope, potentially slowing down the search operation and returning too many results. Starting a search with a wildcard, in particular, can be very inefficient.
C. Use searches against single Objects for greater speed and accuracy.

Searching against a single object, rather than multiple objects, can improve both the speed and accuracy of the search results. Narrowing down the search to a specific object limits the amount of data that SOSL needs to scan, resulting in faster and more relevant search outcomes.

The answer should be A and C. B is not, if you use Find IN ALL Fields, that will definately slow the searching.