When discussing tuned circuits, selectivity is related to Q or bandwidth, which is measure of passing a desired signal while rejecting others that are either higher or lower in frequency
Sensitivity is related to the smallest amplitude signal that can be detected.
Sensitivity is usually limited by thermal noise; not by lack of gain.
Thanyou so much! I went through 3 books in 1 hour and they said nothing about sensitivity other than just mentioning it like I already new what it was,but would go into great detail about selectivity.