試題詳解

73. Clams and lobsters both have exoskeletons, but lobsters have much greater mobility. Why?

(A) The lobster skeleton can actively contract, while the clam skeleton lacks its own contractile mechanism.

(B) Clams only have adductor muscles that hold the shell closed, whereas lobsters have both abductor and adductor muscles.

(C) Clams can only grow by adding to the outer edge of the shell, whereas lobsters molt and repeatedly replace their exoskeleton with a larger, more flexible one.

(D) Lobsters have a jointed exoskeleton, allowing for the flexible movement of appendages and body parts at the joints.

(E) The paramyosin of clam muscles holds them in a low-energy state of contraction, whereas lobster muscles are very similar to vertebrate striated muscles.