"A heavy rain" should also be accepted. I've just reported it.
rain is uncountable, so you can't use a singular article with it
This may be a difference in regional dialects but many people do indeed say "a heavy rain," usually in reference to a specific incident, such as "we had a heavy rain last week."
Is "big rain" wrong in English?
I was marked wrong for "a big rain", which is a rain which has finished, so not necessarily the same as a heavy rain, as it may have rained fairly lightly for a long time.
Not many people say big rain. Well not many people say it in Minnesota so maybe in other places.
heavy rain, but what about "heavy rains?" from what I can tell this is a NC 9/10 so is both singular and plural??
David Cage, is that you?