Which molecule blocks the myofilaments, actin and myosin, from interacting, and how is it moved when you want to contract a muscle

tropomyosin

Explanation:

Tropomyosin is an elongated (α-helical coiled-coil) molecule that controls muscle contraction by blocking the binding of myosin to actin, thereby preventing cross-bridge formation required for muscle contraction. Tropomyosin is removed during muscle contraction, which is initiated by the release of calcium ions (Ca 2+) from the sarcoplasmic reticulum. Moreover, the complex troponin (composed of troponin C, troponin I, and troponin T proteins) binds to tropomyosin and helps to localize it on the actin filament.

the correct answer, according to e2020, is the second choice there is an occluded front in region a and a cold front in region b.

a- all cells come from pre-existing cells