"I am drinking alcohol."
I am not sure why this pops up in the English forum for speakers of Dutch, but I will try to answer your question.
Your answer is not accepted because the structure of the continuous is different in French and because you leave out the article. A correct answer would be "Je suis en train de boire de l'alcool". This structure will be taught later in the course so don't worry too much about it as you can just say "je bois de l'alcool".
French uses the articles du/de la/de l'/des in places where you wouldn't use an article in English. For example, "I am eating bread" translates to "je mange du pain" in French, and "she has cats" translates to "elle a des chats".