Which best compares AC and DC?

a
AC flows in one direction, and DC repeatedly switches direction.
b
AC is used only in generators, and DC is used only in motors.
c
DC is used only in generators, and AC is used only in motors.
d
DC flows in one direction, and AC repeatedly switches direction.
Please Help me, I have no clue what I'm reading, and I'm trying to make a good grade on this formative assesement

B) DC flows in one direction, and AC repeatedly switches directions.

Explanation:

DC stands for direct current, which is a current that constantly flows in only one direction.

AC stands for alternating current, which is a current that repeatedly changes directions.

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  the   balanced   equation   for   reaction of   ca metal   with   o2 to   produce   cao   is as below

2 ca+ o2→ 2 cao2

  explanation

the reaction is   balanced     since the   number of atoms   in reactant side is   equal to   number of atoms   in   product side.   for   example   they   are 2   atom of   ca in   reactant   side   and   2   atoms of ca   in   the product side.

  the   process   is a   meet the   requirement   of   redox   reaction because :     calcium   is   oxidized   from   oxidation state 0   to 2+   while   oxygen   is reduced from   oxidation   state   0   to 2-

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the atomic number of carbon is six, which means that a carbon atom has six protons. carbon has three naturally occurring isotopes: carbon-12, carbon-13, and carbon-14. which of these statements are true about carbon and its isotopes? select all that appl