Four Colombian police officers are dead and at least five more wounded after leftist rebels ambushed a police patrol in the _______ part of the country.

A．competitive
B．controversial
C．distracting
D．irrational

A．Wearing arm weights while you are swimming.
B．Jogging vigorously in one place for a long time.
C．Using bicycles that require you to use both your arms and legs.
D．Walking slowly while swinging your arms back and forth.