A reliable way to check a tricky spelling is to break the word into its syllables and test each option against that pattern, rather than just eyeballing the choices.
The correct word "renaissance" splits into four sound units: re - nai - ssan - ce.
Testing each option against this pattern:
"rennassance" fails at the first unit itself, it has "renn" (double n) instead of "re" (single n), and it is also missing the "i" sound in the second unit.
"renaissance" matches the pattern exactly: "re" (single n), "nai" (with the i), "ssan" (double s), "ce".
"rennaiscence" gets the first two units wrong in the same "renn" way, and additionally changes the ending sound from "ssance" to "scence", which is not part of this word at all.
"rennaissance" gets every unit right except the very first one, where it wrongly doubles the "n" to give "renn" instead of "re".
Since only "renaissance" satisfies the full re-nai-ssan-ce pattern, option B is confirmed as the correct spelling.
Let's summarize:
This syllable-check method works for most commonly confused spellings, not just this one.