—_________ on historical facts, it's well worth reading.
| A．To base | B．Having based |
| C．Basing | D．Based |
You ____ television．Why not do something more active?
| A．always watch | B．are always watching |
| C．have always watched | D．have always been watching |
She is my best teacher ______ help I have made great progress．
| A．with whom | B．whose | C．which | D．with whose |
E-mail, as well as telephones, ___ an important part in daily communication.
| A．have played | B．is playing | C．are playing | D．play |
In order to make our city green, _________.
| A．it is necessary to have planted many trees | B．many more trees need to plant |
| C．we must plant more trees | D．our city needs more trees |
He was about to tell me the secret _______ someone patted him on the shoulder.
| A．as | B．until | C．while | D．when |