how do I identify the functional groups/compounds in the following question?

[SWinchester]

Hello, my teacher gave me this question and seems like none of my classmates know the answer. I understand that first I have to find a compund that reacts with HCL to find the first letter "A" but how do I do that? Thank you in advance for the ones willing to help me

 

Compound X was treated with Hydrochloric acid to give compound A, a primary substituted compound. Compound A was then treated with aqueous sodium hydroxide to give compound B and sodium chloride as products.
Compound B was oxidized to compound C which was further oxidized to
compound D. Compound D was found to have a formula of C₃H₆O₂
and had a pH <7. Compounds B &
D reacted with one another in the
presence of an acid catalyst to give compound E (which had a strong odour) and water. Compound F was produced when compound A was reacted with ammonia.

 

[Fuzzwood]

What can you deduce from the fact that you get sodium chloride in the 2nd reaction?