a. This statement is correct.
Explanation
Veto power refers to the exclusive privilege enjoyed by the 5 permanent members of the UN Security Council. It is the power to vote against any substantive resolution. The permanent members are the US, the UK, Russia, China and France. It has allowed the world powers to wield authority and power and dominate the proceedings of the UN.
b. This statement is correct.
Explanation
It is negative voting against the draft resolution which has given an additional advantage to the 5 permanent members to stall any decision of the UN. The veto power is argued to be the most undemocratic instrument that creates a permanent hiatus between the members of the UN.
c. This statement is wrong.
Explanation
The Secretary-General is the head of the UN Secretariat and the de facto spokesperson. He/she is rather appointed by the General Assembly on the recommendation of the Security Council, and he is dependent on the support extended by the members of the UN.
d. This statement is correct.
Explanation
Permanent members have always used the veto power in their own interests and not in the interests of the global community at large. For example, we may talk about how the veto power became a tool in the hands of the US and the USSR during the Cold War, where it became difficult to reach at a consensus.