. The glass doors have taken the place of the wooden ones at the entrance, __________ in the natural light during the day.
| A．to let | B．letting |
| C．let | D．having let |
I don't know whether the books __________ to the homeless children next month are really useful.
| A．given | B．to be given |
| C．giving | D．which were given |
There was no more than one iPhone 4S in the store, so I had no choice but __________.
| A．take | B．taking |
| C．taken | D．to take |
The machine has been made easier for it __________.
| A．to operate | B．operated |
| C．being operated | D．to be operated |
No matter how bright a talker you are, there are times when it's better __________ silent.
| A．remain | B．be remaining |
| C．having remained | D．to remain |
I remembered __________ the door before I left the office, but forgot to turn off the lights.
| A．locking | B．to lock |
| C．having locked | D．to have locked |