Which of the following constitutes plagiarism $($check all that apply$)?$

a$)$ representing someone else's work as your own without acknowledging the source

b$)$ using another's words and giving credit but doing so incorrectly

c$)$ employing an assignment writing service or having someone else write a paper for you

d$)$ submitting or reusing parts of a paper that was previously submitted for another course

e$)$ none of the above