While we were running on the playground,Jack suddenly stopped ___________ and lay on the ground,so we all stopped ___________ what was wrong with him.

A．running; to see

B．running; seeing

C．to run; to see

D．to run; seeing

下列叙述不属于金属物理性质的是（　　）

A．铜是紫红色的金属

B．铁有良好的导电性

C．晶态的银呈银白色，原子态的银呈黑色

D．加热铜片使其表面变黑