"You come from Italy."
Translation:Ab Italia venis.
a is only used in front of consonants.
ab is used in front of vowels and 'h' (and sometimes other consonants).
If you want an in depth look at the forms of a/ab and how they are used you can read here: http://www.perseus.tufts.edu/hopper/text?doc=ab&fromdoc=Perseus%3Atext%3A1999.04.0059
Yeh, this one is straight up wrong. Ab Italia venitis (You-plural come from Italy) should be accepted, as the subject number is not clear here. This is especially true when using the word bank, where "venitis" is even one of the suggested words!
And before you ask, yes, I reported it.
The pronoun should not be included, except when for emphasis; doing this at this level is entirely due to the design of the course, teaching it at beginner’s level as though this was the normal way for Latin speakers and writers to express themselves. The same problem goes for the verb; it should be put at the end, which was by far the most common. This leaves ‘Ab Italiā venis.’ I do believe your answer should be accepted, though with a comment labeling it as having an unusual structure.