The subject of a sentence cannot be a noun clause.

a. True

b. False

Its false. it can be a noun phrase

e. g

the book belongs to Sara.

in this sentence "the" is determiner (article) used to highlight the specification of book (the subject in the sentence) which belongs to a specific person Sara.

together they (the and book) make a noun phrase.

hope you understand the thing

b. False

The subject of a sentence can be a noun clause.