NCERT Class 9: Democratic Politics page 87:"Since it is not practical for all ministers to meet regularly and discuss everything, (hence) the decisions are taken in Cabinet meetings. That is why parliamentary democracy in most countries is often known as the Cabinet form of government." Therefore, some expert felt that cabinet form of Government helps in work distribution and thereby speeding up efficiency so b is the right answer. However, other experts went by the interpretation given in M.Laxmikanth's book on Indian Polity:"Parliamentary system is also known as Cabinet Government. It provides for collective responsibility of the executive to the legislature." so c should be the answer. UPSC has kept ' "c" as the official answer.