It's an electronically synthesized voice. I think it's remarkable that it's able to convey emphasis and accent reliably at all. So it's not a woman with thoughts and feelings, it's a robot. DL could give us the option of selecting an equally dispassionate "male" robot quite easily.
Not exactly... you have that "stern voice" where the person that is delivering the command's voice drops dramatically. You know what I'm talking about. You know, the type of voice that scares your inner rebel. Or, if you wish, you could think of it as "Do. Not eat. My. Candy.", although Duolingo would most likely think you have issues if someone was sitting behind the screen.
The problem is that English distinguishes between count nouns and mass nouns. Candy is usually mass: a little candy, a lot of candy, a piece of candy - Don't eat (any) candy before dinner; BUT it can convert to a count noun: one candy, two candies, many candies. Some nouns cannot do that (e.g. water is always mass: a lot of water, a cup of water); or, if they do, it changes the meaning: give me two waters (= two bottles of water, or 2 kinds/brands of water). British English is clearer with "sweets" as the preferred term, a plural count noun used for the general.
What is the problem? In America, we say "candy" to indicate candy in the plural. "How much candy did you get?", "Where's the candy?" Does not refer to one candy. It reders to a stash of candy. A pile or bowl of candy. We never say "candies". I grew up in America and never once heard plural candy referred to as "candies". Hope this helps!
Because in American English "candy" is a mass noun: https://en.oxforddictionaries.com/definition/candy
This question has been asked many times. It seems Americans use "candy" as a mass noun, so that they have one candy in the box or ten candy in the box. It sounds very odd to non-Americans but there you go. Such is life. Roll with it and accept that the language used is American English, and the lessons are free. I decided to save my annoyance for things that actually matter, even though it gives me indigestion to write "candy" and "cookie".