They can't even play, ____ writing their own songs.
a. less likely
b. not to mention
c. let alone
d. needless to say
I am familiar with these expressions but not to the extent to tell the differences.I don't know what the sentence implies differently if I chose one to another.When I scanned some grammar resources again I found that let alone is mostly used in negative sense and it seems like when let alone is used whole sentence focus to the same person and related process.This is my humble interpretation.
For example (Longman)
The baby can't even sit up yet, let alone walk.
But lets say we visited a city for the first time and the city didn't live up to our expectations , would it be more accurate to say :
The food is terrible , not to mention its the crowded streets.
Because we mention two different aspects of the city or our experience.
So I'd like to ask what the sentence imply for each option if it makes sense to use all.
b. is correct.
The form of this should be "less likely than/that" (than/that as conjunctions) since you are making a comparison.
The example does not have a conjuction to use, so a. is incorrect.
Here you would use the same verb form in the connected phrases, so for c. to be correct, the example would have to be:
is usually not used in connecting phrases. An example: