Of the 9,500 drivers ____ since the beginning of the year, 23% were found ____ in road knowledge.

A．tested; lacked

B．testing; lacked

C．tested; lacking

D．to test; lacking

已知一个数由3个千万、6个十万、7个百和5个一组成，那么这个数写作______．它是一个______位数，这个数也可以看成由______个万和______个一组成．