Lucy ________ guitar lessons every three weeks in the past three years, but now she is considering she'll make it every other week.
| A．is having | B．had had |
| C．had | D．has been having |
We can’t figure out ______ quite a number of insects and birds are dying out．
| A．that | B．as | C．why | D．when |
______ environmental damage is done，it takes many years for the ecosystem to recover．
| A．Even if | B．If only |
| C．As if | D．Once |
Spending a few hours learning about the history and culture of the destination will help tourists understand they're seeing
| A．what | B．where |
| C．that | D．why |
—Sarah went to the party．
—Really? I her if I had gone with you．
| A．met | B．had met |
| C．would met | D．would have met |
—Good news ! There's a supermarket in this area next month!
—Cool! It will be convenient for us when it's open
| A．building | B．built |
| C．having built | D．to be built |