28. Vitamin D helps our bodies make a special chemical, and this special chemical, _______, affects our brains, making us feel happy.
Nobody could believe what Chloe says because she is ______ changing her mind.
Don't ______.You will ______ new customs and different ways of thinking.
It______ a calm head to find the best solution to such a difficult problem within a short time.
By the end of 2007,about half a million people had flooded into the city,______ up around 10 percent of its total population.
Jumping out of ______ airplane at ten thousand feet is quite ______ exciting experience.