"He is a boy and he is calm."
Translation:C'est un garçon et il est calme.
C' is neutral, when the sentence identifies the gender such as he is a boy or she is a girl, french use C'est (she/he is) it's just one of the rules. Once the gender has been identified in the sentence (he is a a BOY...) then that gender's usual il/elle is then used..he is a boy and HE is calm
I'm not sure about the mobile-app, but the web-app provides this guidance for this topic: https://www.duolingo.com/skill/fr/Gallicism%3Ail-elle-OR-c-ce/tips-and-notes
"il/elle est" and "ils/elles sont" change to "c'est" and "ce sont" before a modified noun, that is, a noun preceded by a modifier. A modifier can be:
- an article: un, une, des, le, la, l', les
- a number: un, deux...
- a possessive adjective: mon, ton, son, ma, ta, sa, notre, votre, leur, mes, tes, ses, nos, vos, leurs
- a demonstrative adjective: ce, cet, cette, ces
These articles go into more detail and are worth a read.
Also, the Tips and Notes for the Gallicism skill (click the lightbulb icon when you open the skill) give more information.
I'd recommend taking a peek at the advice offered here: https://www.duolingo.com/skill/fr/Gallicism%3Ail-elle-OR-c-ce/tips-and-notes
If you want my shorter, less trustworthy version, here it is:
1) If you simply want to state that she/he is calm (or tall or some other adjective), use Elle/Il est:
- Elle est calme.
- Il est calme.
- Elle est grande et calme.
- Il est some-adjective(s).
2) In all other cases involving "She/He/It is ...", use C'est:
- He is a calm boy. -> C'est un garçon calme.
- He is a boy. -> C'est un garçon.
- It is brief, simple, and incomplete. -> C'est bref, simple, et incomplet.
Please note that (1) and (2) oversimplify things! I'm telling you, this is just one amateur's quick/simple distillation of the more trustworthy https://www.duolingo.com/skill/fr/Gallicism%3Ail-elle-OR-c-ce/tips-and-notes
Duolingo normally puts all translations that are possible for a specific word, but it doesn't necessarily mean each answer is correct, it depends on the context. In the case of "he is a boy" it needs to be "c'est un garçon," because there is an article (un) present. Duolingo does have notes on this if you need more explanation. I hope this helps :)
That order cannot work, unfortunately. The rule is that if there is a article (le, la, un etc) or a possessive adjective (mon, ses, etc) one needs to use "c'est." When there is an adjective or adverb after "être" then a personal pronoun (il/elle or ils/elles) needs to be used. If you wrote "c'est calme" you are taking about something in general, but not necessarily the person. Hope that helps. All this info can be found in the notes on Duolingo.