Explanation : We can generate more than 1 parse tree for a single string from the grammars. For statement (iii)
S → U
U → yT
yT → yxSy
yxSy → yxTy
yxTy → yxxyy
All statement are correct. So, option (D) is correct.
Parser is a part of compiler and responsible for syntax recognition. Scanner (or tokenization) used by lexical analyzer. In Semantic analysis consistency and definition of syntax is checked. An optimizer is used improve the IR program. So option (A) is correct.
Explanation : In C-SCAN disk scheduling algorithm, the disk head serve the request from one end to other end but when it reaches to other end it immediately returns to the starting of the disk without serving any request.
So option (D) is correct.