题干
________is well known to all that Barack Obama will keep his promise___________he will remove the military forces from Iraq.
A：As, which
B：It, that
C：What, that
D：It, which
答案(点此获取答案解析）
B
≤a(x+y)对一切正数x、y恒成立，则正数a的最小值为（ ）