What is the default queuing mechanism on slow serial interfaces?

A.
FIFO

B.
WFQ

C.
CQ

D.
LLQ

E.
WRR

Explanation:
http://www.cisco.com/en/US/docs/ios/12_2/qos/configuration/guide/qcfconmg.html#wp1001019
Given this handling, WFQ ensures satisfactory response time to critical applications, such as
interactive, transaction-based applications, that are intolerant of performance degradation. For
serial interfaces at E1 (2.048 Mbps) and below, flow-based WFQ is used by default. When no
other queueing strategies are configured, all other interfaces use FIFO by default.