I believe it is B i took this test last year.
The main responsible for the delay among the atrial and
ventricular contractions is the action potential conduction velocity of the AV
node cells. If the atria and ventricles contract simultaneously, atria cannot
give any help in filling the ventricles, which is needed, especially in those
with stiff ventricles as in the elderly. Hence atria have to contract first and
then the ventricles.
When plates divide or separate it creates a divergent boundary.
The core, or middle, of the Sun is the hottest part. Hot gasses bubble up from the core to the surface of the Sun. When the gasses burn, heat and light are produced.
<span>cells are the units of structure and different functions in livings things
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