(a) Bed rock
(b) Moho
(c) Benioff zone
(d) Lithosphere
Ans :- (b) Moho

Explanation :-
The boundary between the crust and mantle is called as Moho or Mohorovicic discontinuity boundary.

• It’s depth lies of about 22 mile (35 km) continents and 4.5 mile (7 km) beneath the ocean current.
• It is made up of elements such as oxygen, Iron, Sodium Silicon & Aluminium (SIAL).