31. In the past few years, research has suggested that Vitamin D may increase the level of serotonin(血清素), one of the key neurotransmitters influencing our mood, and ________it helps to relieve mood disorders.
Martin Luther King Jr.was _____ the Noble Peace Prize of 1964 for advocating nonviolence policy in the movement for civil rights.
The income of skilled workers went up.______, unskilled workers saw their earnings fall.
I’m sure that your letter will get ______ attention.They know you’re waiting for the reply.
It seems that living green is _____ easy and affordable.A small step makes a big difference.
My uncle’s house in the downtown area is much smaller than ours, but it is twice ____ expensive.