What is a major cause of the Earth's magnetic field

The Earth's magnetic field is mostly caused by electric currents in the liquid outer core. ... Convection of molten iron within the outer liquid core, along with a Coriolis effect caused by the overall planetary rotation, tends to organize these "electric currents" in rolls aligned along the north-south polar axis.

Explanation:

Electric currents in the liquid outer core are primarily responsible for the Earth's magnetic field. Convection of molten iron within the outer liquid core, combined with the Coriolis force generated by the total planetary rotation, tends to organize these "electric currents" into rolls lined north-south along the polar axis.

in the following paragraph, the fourth sentence the correct answer is: three personal subject pronouns

”she was embarrassed when she found that they had been put back on the shelves…”

a   subject pronoun is a personal pronoun. i, you, he, she it, we, they.  

in the sentence it can be observed she, used twice and they used once. is for this reason that is a three personal subject pronoun sentence.