Which two protocols are used by bridges and/or switches to prevent loops in a layer 2 network?

Which two protocols are used by bridges and/or switches to prevent loops in a layer 2 network?
(Choose two.)

A.
802.1d

B.
VTP

C.
802.1q

D.
STP

E.
SAP

Explanation:
This question is to examine the STP protocol.
STP (802.1d) is used to prevent Layer 2 loops.
802.1q is a Frame Relay protocol which belongs to VLAN.
SAP is a concept of the OSI model.