これは - this は marks the topic of the sentence, and from what comes later we can tell that it’s something the speaker and listener can both see
私が - here, が marks the subject in the clause 去年私が海でとった
海で - the function of で here is to mark the location where the action (とった) took place
The clause modifies しゃしん, explaining what kind of picture it is (a picture that I took at the sea last year)
Factoring in the whole sentence, we have “This is a picture that I took at the sea last year.”
So the 去年 is not part of this clause? It seems kinda shoehorned in there, is there any reason why they don’t say for example 去年に or 去年の? It’s hard to figure out how it relates to the rest of the sentence.
It is, I was just stripping it down to the parts necessary to explain the grammar of the clause. I edited the post. Relative time words like 去年 require no particle. Just like we don’t say “On/in last year” in English.
You’re technically not allowed to share questions from the test… But the time period of that being relevant is like… The 24 hours when the test is being administered around the world. Not months or years later. No one cares at that point.