"the" vs "a" on TOEIC tests

There is a section in the TOEIC Speaking & Writing Test where you are supposed to describe a picture.

Let's say there is a picture of a man holding a cell phone at a refinery (an example question from the internet).

I would write: A worker is holding a cell phone at a refinery.
But the example answers always had "the" instead of "a" (as in "the" worker is holding a...)

I think both articles suffice for answering, right?

On another section, you are asked to write a sentence based on two words given and a photo.

Pies & breakfast are the words with a photo of pies on a table.

If I write "I had pies for breakfast" instead of "Pies are given for breakfast," would I be wrong?

I wonder how much flexibility is given for the answers.

Thanks in advance.