"stream piracy"
choose one:
a. can leave behind a dry channel through a high ridge called a water gap.
b. results when headward erosion causes one stream to intersect the course of another stream.
c. causes the pirate stream to decrease its discharge and eventually dry up, while the captured stream continues flowing.
d. occurs frequently throughout recorded history, with a case reported in 2016 in the yukon.

B. Results when headward erosion causes one stream to intersect the course of another stream.  

Explanation:

Headward erosion of a low level stream can extend to intersect a higher level stream and draw away its water.

The diagram below shows Stream A eroding headward into Stream B and capturing its water flow.

A.is wrong. A water gap still carries water today.

C. is wrong. The captured stream dries up, while the pirate stream increases its flow.

D. is wrong. A dramatic example did occur in the Yukon in 1916, However, stream captures do not occur frequently.