The International Monetary Fund provides short-term loans mainly to stabilize the international exchange rate.

"The weight of RMB ranks third after the US dollar and the euro", which shows that this move is an important milestone for China's economic integration into the global financial system. B is correct and does not conform to the meaning of the question;

The weight of the dollar comes first, so the United States plays an important role in the SDR currency basket. C is correct and does not meet the meaning of the question;

The International Monetary Fund belongs to the international monetary and financial system, so its funds can be used for international cooperation in the financial and monetary fields.

So choose a.