The correct option is A True
A noun clause is a dependent clause that functions as a noun. It usually
begins with what, whatever, whom, that and other such relative
pronouns. A noun clause can act as a subject, object, predicate
nominative or object of a preposition, in a sentence.
The noun clause "who you saw last" is the direct object of the verb "tell", the subject is implied as 'you'. (When a sentence begins with 'please', the subject is usually implied as 'you'.)
Hence the statement is true and option A is correct, B is incorrect.