As a result of a supernova explosion, every human being on Earth was bombarded on February 23, 1987, by about 100 billion neutrinos; fortunately, neutrinos are harmless elementary particles that are produced in nuclear reactions and that interact very weakly with matter

(a) neutrinos are harmless elementary particles that are produced in nuclear reactions and that
-> correct (best among 5)

(b) neutrinos, which are harmless, are elementary particles produced in nuclear reactions and which
-> Incorrect parallelism

(c) neutrinos are harmless elementary particles produced in nuclear reactions and which
-> "which" should be separated by comma

(d) these harmless elementary particles are produced in nuclear reactions, and neutrinos
->first "these harmless elementary particles" and latter on neutrinos
-> comma before "and" not needed

(e) these elementary particles, harmless products of nuclear reactions, are neutrinos that
-> same as D; Interchange of " these elementary ... neutrinos"


One use of that -> introduce restricted clause.

"which" always start with comma and end with comma as "which" is a non-restrictive clause.