下列有关化学基本概念的判断依据，正确的是（ ）
| A．溶液与胶体：本质区别是否均一、透明 |
| B．纯净物与混合物：是否仅含有一种元素 |
| C．氧化还原反应与非氧化还原反应：元素化合价是否有升降 |
| D．电解质与非电解质：物质本身是否导电 |
Progress______ so far very good and we are sure that the work will be finished on time.
| A．was | B．had been | C．has been | D．will be |
Charles was alone at home, with_______ looking after him.
| A．someone | B．anyone | C．not one | D．no one |
It is often ______ that human beings are naturally equipped to speak.
| A．said | B．to say | C．saying | D．being said |
I can’t leave. She told me that I ______ stay here until she comes back.
| A．can | B．must | C．will | D．may |
—— Do you mind my opening the window? It’s a bit hot in here.
—— ______ , as a matter of fact
| A．Go ahead | B．Yes, my pleasure |
C．Yes, I do | D．Come on |