So here we have an example problem that asks, which of the following is not a mechanism used by the lymphatic system to propel lymph. And we've got these 4 potential answer options down below. Now, option A says, pulsation of nearby arteries, and the pulsation refers to the rhythmic contraction and dilation of these arteries. And recall from our last lesson video that this was one of the mechanisms that we listed that can help propel lymph through the body. And so for that reason, we can eliminate answer option A, since, again, we're looking for the option that is not a mechanism that propels lymph. Now moving on, option B says contraction of nearby skeletal muscle, and this is probably the most effective means of propelling lymph through the lymphatic system. And so option B certainly is a mechanism that propels lymph, so for that reason we can eliminate answer option B.

Now, option C says, contraction of cardiac muscle allows the heart to serve as a pump for lymph. However, recall from our last lesson video that unlike the cardiovascular system, the lymphatic system does not have a pump that propels the fluid. And so, although the heart does serve as a pump to propel blood through the cardiovascular system, the heart does not serve as a pump to propel lymph through the lymphatic system. So for that reason, we can indicate that answer option C is the option that is not a mechanism used to propel lymph through the lymphatic system. So option C is the answer that we are looking for, so we can indicate C here is the correct answer.

Now option D says contraction of smooth muscle, and we can eliminate this one as well because recall that the larger lymphatic vessels can have smooth muscle in their walls that can contract to help propel lymph, and so, we can eliminate option D. Again, C is the correct answer. That concludes this example, and I'll see you all in our next video.