The London 2012 Olympic Games marks the third time that London ________ the right to host the modern Olympics.

A．had had

B．has

C．had

D．has had

纳米是一种长度单位1纳米=10^﹣9米．已知某种植物花粉的直径约为35 000纳米，那么用科学记数法表示该种花粉的直径为[     ]

A．3.5×10⁴米

B．3.5×10^﹣4米

C．3.5×10^﹣5米

D．3.5×10^﹣9米