Question

The single most important ingredient in a good beer is high-quality

Answer 1

The single most important ingredient in a good beer is high quality WATER. The correct option is D.
The quantity of water in beer is more than 90%. High quality water is the most important ingredient that is required in beer making process. 
After water comes barley malt, hops and then yeast respectively.

Answer 2

the main ingredient is Malt

Yeast is for the fermentation

Hops mainly for the taste

Water is 95% of this beverage.....but is it considered as a main ingredient...in quantity yes, but it doesn't make a beer !!!

hope I helped