a. This statement is correct.
The UN Security Council is the most powerful organisation that comprises 5 permanent and 10 non-permanent members. The main aim of this council is to maintain international peace and security and to deal with other security matters. It also investigates and recommends peaceful resolution of conflicts among the nation states.
b. This statement is correct.
The UN and its agencies, ever since their inception, have played a proactive role in the field of health, education and human rights for providing all humanitarian assistance to the community. Examples include ILO, UNESCO and UNHCR.
c. This statement is correct.
Since the main role of the Security Council is to deal with matters related to international peace and security, it is imperative for the 5 permanent members of the UN to reach at a consensus among themselves. Any military action or imposition of sanctions on any nation state has to be endorsed by these permanent members.
d. This statement is wrong.
The UN General Assembly represents a World Parliament that comprises representatives from all the member states with each having one vote. The assembly discusses, deliberates and debates on the issues of global interests allowing all the representatives to freely present their views. The UN Security Council, on the other hand, has 5 permanent and 10 non-permanent members, elected for a period of 2 years. The members are elected such that they can represent all the continents of the world.