Which two protocols can be automatically negotiated between switches for trunking? (Choose two.)

A.
PPP

B.
DTP

C.
ISL

D.
HDLC

E.
DLCI

F.
DOT1Q

Explanation:
Switches such as the Catalyst 3550 that are capable of either 802.1Q or ISL trunking encapsulation, the switchport trunk encapsulation [dot1q | isl | negotiate]
interface command must be used prior to the switchport mode trunk command.
https://learningnetwork.cisco.com/servlet/JiveServlet/previewBody/14792-102-1- 57313/Dynamic%20Trunking%20Protocol.PDF