In the system labels b in figure 27-11, where does oxygen-poor blood go after leaving the heart? why?

Oxygen-poor blood goes into the lungs and through the lung capillaries after leaving the heart. It does so to be oxygenated by the lungs. The oxygen in the lungs comes from the air we breath. Once the blood is oxygenated, it goes back into the heart, to be pumped back into our bodies for distribution. 

Nimbostratus is the correct answer.
explanation: nimbostratus clouds are the type of clouds that are mostly likely present on gray, rainy day. these clouds produce continuous rain, snow and there is no thundering or lightening either.