In the past few years, research has suggested that Vitamin D may increase the level of serotonin（血清素）, one of the key nurotransmitters influencing our mood, and ________it helps to relieve mood disorders.
| A．that | B．where | C．what | D．which |
IP addresses are the unique sequence of numbers ______ to each computer, websites or other Internet-connected devices.
| A．to assign | B．assigning |
| C．assigned | D．being assigned |
— Do you have the time? I’ve got something to tell you.
— Ok, ______ you make your story short.
| A．now that | B．even if | C．so long as | D．in case |
On top of the hill ______, whose style can be traced to the ages of the Roman Empire.
| A．there standing a church | B．does a church stand |
| C．a church stands | D．stands a church |
A warning signal suddenly appeared on the screen of my computer, ______ the computer was being attacked by a certain virus.
| A．indicated | B．indicating |
| C．to indicate | D．having indicated |
Something has to be done to stop the rivers from being further polluted, ?
| A．doesn’t it | B．hasn’t it | C．does it | D．has it |