1) What does "this" refer to? Choose the idea that completes the sentence.
This leg was specifically designed for rock climbing and has
many features that can help the climber, such as the spiked
foot, which grips the rock face better than any biological foot
could. Other prosthetics can help people excel at the sports
they love, too.
Engineer Hugh Herr has made this his life's work.
Engineer Hugh Herr has made
his life's work.
D) discovering challenging rock faces
teaching rock climbing
strengthening biological limbs
designing prosthetic limbs