Compared to permanent magnets, why are electromagnets more useful in many modern technologies?
O A. In permanent magnets, the strength of the magnetic field is more
consistent.
O B. To use an electromagnet, a power supply is not necessary.
O C. Strong permanent magnets are too large to use.
O D. By controlling the current, electromagnets can be turned on and
off.

answer; /// the above statement is (true);

answer: i don't know the answer good luck

explanation:

as we probably am aware that our atmosphere or air have various levels, each level has different gasses, and each gas has another porousness. at the point when the light originates from lower porousness to higher penetrability, it alters its course. with the goal that implies that when the light originates from the moon to the earth, it alters it's course a lot more occasions. it essentially implies that the state of the light piece of the moon is changed on the earth.

not copied too! hope this !

joke:

h o h o hope you have a merry christmas!