Why does white water rafting damage river and streams? a) the raft decreases the current within the system. b) the presence of humans decrease the available oxygen in the ecosystem. c) riverbeds are dredged to eliminate hazards. d) the presence of humans scare off aquatic life. e) photosynthetic rate is decreased.

Cancer cells spread to other parts of the body by entering the bloodstream. which of the following organs could prevent a cancer cell in the bloodstream from spreading, and why? a. the spleen, because it releases lymphocytes into the blood b. the peyer's patches, because they release lymphocytes into the blood c. the lymph nodes, because they release lymph into the blood d. the thymus, because it releases lymph into the blood