Dear teachers,
Do we the article " the" before violin in the following sentence? Please advise, thanks very much.
Mozart could play the piano and (the???) violin by the time he was six.

I could bath by myself without my parent's help when I was two. ( Is this sent grammatically correct?)

Is there a difference in meaning to the sentences below? Which one is correct?

A. Mozart composed a lot of church songs when he was working as the concert master in Salzburg.

B.Mozart composed a lot of church songs when he worked as the concert master in Salzburg.
For Q3, there is a difference in meaning, though the difference is subtle. "He was working" implies progressing action, wheras "he worked" implied completed action. In the context of the wider sentence, I would prefer A over B, for this reason - B almost suggests that he started composing when he got to work, and stopped composing when he finished work, wheras A is a bit more flexible.

I would also change the word "when". Replace it with "while" (American) or "whilst" (British).

I am not a teacher but I will try to help, if you would like.
In Q1, I would not put a "the" in front of violin. It is a fact of parallelism it sounds like to me.

In Q2, I would phrase it like this but this is for reference:
--> When I was two, I was able to bathe (not bath) myself. It is implied when you say myself that you were not being helped by your parents. Hope you understand.

In Q3, you are saying the same thing in each sentence. Instead of "a lot of", I would use many. Was working is past tense and worked is also past tense. You are just saving words by using the second one.

Hope this helps...
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 rommie's reply was promoted to an answer.
I agree with Rommie with respect to Q3 and would favour 'whilst he was working' (being British!).

Regarding Q1 it's down to personal preference, you might utilise 'the' twice by saying 'played both the piano and the violin'. This then has similar meaning to 'not only the piano but the violin also', emphasising Mozart's ability.

Without the article before violin, it reads more like a list of instruments that Mozart could play to which others could be added without additional articles; 'played the piano, flute, oboe and violin'.

NB I have no idea whether Mozart could play the flute and oboe but would not be at all surprised to learn that he could.