Aluminum isn’t found free in nature, owing to its always ____ with other elements, most commonly with oxygen.
| A．being combined | B．having combined |
| C．combine | D．combined |
He ran off____ I could stop him.
| A．before | B．after | C．since | D．when |
We should pay attention ____ to industry ____ to agriculture.
| A．either, or | B．neither, nor | C．not, but | D．both, and |
My sister is expecting me,____ I must be off now.
| A．however | B．or | C．so | D．otherwise |
Do not make the same mistake ____ I did.
| A．so | B．as | C．like | D．that |
Hurry up, ____ you'll be late.
| A．or | B．and | C．so | D．yet |