Antidepressant drugs have been designed to increase levels of serotonin and question 41 options:

Antidepressant drugs have been designed to increase levels of serotonin and norepinephrine. Serotonin is a hormone that is responsible for the regulation of our mood , anxiety and happiness. Norepinephrine is also a hormone that is secreted as a response to stress. It is deemed to be similar with the hormone adrenaline. Low levels of these hormones are associated with depression. Antidepressant drugs works in increasing the levels of these hormones to cure or treat depression. However, these drugs do not necessarily cure depression, they are only effective at improving the mood and relieving some of the symptoms along with it. 

The answer id letter d 90