粗盐提纯实验中，除去NaCl中含有的Ca2＋、Mg2＋、SO42-等离子，采用以下四个步骤：①加过量Na2CO3溶液，②加过量Ba(OH)2溶液，③过滤，④加适量盐酸。步骤顺序合理的是
| A．①②③④ | B．③①②④ | C．④②①③ | D．②①③④ |
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 |
It’s high time you had your hair cut ; it’s getting _______ . 
| A．too much long | B．much too long |
C．long too much | D．too long much |
My friend showed me round the town, ______ was very kind of him. 
| A．which | B．that | C．where | D．it |
They use computers to keep the traffic _______ smoothly.
| A．being run | B．run | C．to run | D．running |