Complex sentence: Since PRO is a caseless DP, it can appear in caseless positions, like the specifier of a non-finite Tense Phrase, and helps to account for nonfinite embedded clauses, Carnie, Andrew.
Split into simpler sentences: Since PRO is a caseless DP, it can appear in caseless positions, like the specifier of a non-finite Tense Phrase. It helps to account for nonfinite embedded clauses, Carnie, Andrew.