So difficult ___it to work out the problem that I decided to ask Tom for advice.
| A．I did find | B．did I find | C．I have found | D．have I found |
Students show great interest in ______ Professor Edwards presents to them in his class.
| A．whichever | B．wherever |
| C．whatever | D．however |
—Are you going to the concert next week?
—I’d like to, but I ______ an exam then.
| A．take | B．took |
| C．was taking | D．will be taking |
—I didn’t know you play the piano. It sounds wonderful!
—Thank you! I ______ it when I worked in UK.
| A．learned | B．had learned |
| C．have learned | D．learn |
We are going to the theater tomorrow ______ all the tickets are sold out.
| A．when | B．unless |
| C．whether | D．because |
Once ______, the book will surely attract readers’ attention since it is related to people’s health.
| A．publishing | B．having published |
| C．published | D．to publish |