And yet the postholder of the top job at the United Nations is often asked to provide exactly that kind of all-in-one approach, and is often then blamed for the organisations short-comings. For that reason the job of Secretary General is sometimes seen as one of the most thankless jobs in the world.

Each in turn has been asked not only why they are the most qualified, but also what they would do to realize the trinity of goals of the UN, peace and security, development and human rights.

All of the candidates touched on the hot topics in world affairs, such as the refugee crisis, women's empowerment, peacekeeping and peace building, as well as UN reform. There was also a consensus on one bigger question - how to make the world a safer and more prosperous place eventually?

联合国秘书长候选人关注和平与发展

Natalia Gherman is a former deputy prime minister and foreign minister of Moldova.

"The historic adoption of the 2030 agenda highlighted a longstanding truth that there is no security without development and there is no development without security and there is nothing without respect for human rights. The UN must work harder to deliver the promises of new global partnerships for the citizens of the world."

The 2030 sustainable development is seen as one of the biggest achievements of the UN in recent years.

It is the first global development guideline agreed on by all countries in the history of humanity, with the UN one of its key moderators.

Bulgarian diplomat, head of the UNESCO Irina Bokova argues the common understanding the international community managed to get from the sustainable development document, and the Paris climate pact show the importance of a shared and coordinated vision in addressing global issues.

"But it is known very well that the new challenges which we are confronting these days, refugees, conflicts, the growth of violent extremism, destruction of our heritage, these growing forces want to convince us that we cannot live together. And this is unacceptable for me. I am convinced if we have a common vision on the 2030 Agenda and the climate change agenda, then we will be able to attain sustainable development goals and climate change goals."

Candidate Former Portuguese Prime Minister Antonio Guterres served as the UN high commissioner for refugees for a decade.

"The root causes of conflicts are becoming increasingly interlinked and that is the reason there is a core importance attached to prevention and comprehensive vision. We need to understand the global trends of today's world and find strategies and policies which together can act in line with the UN's three pillars."

All candidates will get the chance to further make their cases at several high-level debates organized by the UN in the coming months, before the Security Council starts the appointment procedure in the summer.

For CRI, I'm Su Yi in New York.