The girl asked, "Could you help me solve the math problem?" "Of course, I can." he replied __________.
Russia is _________ on the north of China.
Lately some scientists are experimenting ___________ white mice to ____________ this kind of medicine.
When the reached the top of the hill ,they _______________ so they had to stop for a rest.
John ____________ his students is playing basketball on the playground.
He does ___________________ that he cannot spare no time to play with his children.