19. Most of the exchange surfaces of multicellular animals are lined with _______. (A) connective tissue (B) smooth muscle cells (C) neural tissue (D) epithelial tissue.

23. The motor (somatic nervous) system can alter the activities of its targets, the skeletal muscle fibers, because _______. (A) it is electrically coupled by gap junctions to the muscles (B) its signals bind to receptor proteins on the muscles (C) its signals reach the muscles via the blood (D) it is connected to the internal neural network of the muscles

19. Most of the exchange surfaces of multicellular animals are lined with _______.
(A) connective tissue
(B) smooth muscle cells
(C) neural tissue
(D) epithelial tissue.

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