'Elastic' goods-is something in the market that is high in demand (in publicity-and that people buy it.
Ex beef is a great example of an elastic good. If you set the beef to a higher price than usual-customers will not buy it as expectedly as before.
'Inelastic' goods like gas- is a perfect example because if you set gas in high price-customers would not question it and pay for the price of gas anyways. (Due to it fulfilling customers' needs only.)
To answer your question, a horizontal demand curve is when you have a fixed demand in price (people are buying it has demand) and that supplies have ample quantity. (Supplies are high quantity)
Demand for a good in the horizontal demand curve is 'moderately elastic' because the supplies have quantity more than the fixed demand. It fits modernly elastic-customers are not buying as much due to high price and therefore supplies of quality increases. Just like the beef example.
The Answer is A
If the horizontal demand curve is 'inelastic' then it would be the opposite- demand would be higher than the quantity of supply.
Hope this helps :)