Even now I am a senior high school student,
I will never forget those days (which were) with wonderful experience!
Even now I am a senior high school student ,
I will never forget those days having wonderful experience!
Using "these" or "those" will depend upon how you feel about it, there is NOTHING wrong to use "these". I change it to "those" just for suggestion only, because I feel that you are desribing "days" that are far away from you.
2012-05-26 00:26:24 補充：
the easiest one is:
(which, that, who, whom, what) + verb (be-V, regular-V ....) + adjective (adverb) + (noun)
2012-05-26 00:30:09 補充：
However, lots of time, these "relative pronoun" can be omitted, and the clause is shortened as "preposition phrase"(like the first one), gerundive phrase (動名詞片語) ...
2012-05-26 03:31:40 補充：
yes, you can write it that way. However, you also need to know that all 3 sentences (which were ..., with ..., having ...) carry slightly different meaning, because their functions in the sentence are different.