The two theories appear to be completely different. (COMMON) → The two theories seem to have nothing in common.

Kiến thức về cấu trúc
Tạm dịch: Hai lý thuyết dường như hoàn toàn khác nhau.
Ta có cấu trúc: have nothing in common = be completely different
=> Đáp án: The two theories seem to have nothing in common.
Note:
Seem to do sth: dường như làm gì

The two theories appear to be completely different. (COMMON) → The two theories seem _______________________.

The two theories appear to be completely different. (COMMON)
→ The two theories seem _______________________.