What Event in 2006 Led to China Allying Itself with the United

What event in 2006 led to China allying itself with the United States, Japan, and Russia?

A) The United Nations inability to curb Iran's nuclear ambitions.
B) The full-membership of China in the World Trade Organization.
C) North Korea's unexpected test of low-grade nuclear weapons.
D) Kim Jong Un's policies that heightened tensions in the Asian region.
E) The al-Qaida terrorist attacks in the US, Europe, and Asia.