Question 1062064
Domain is the set of possible values that can be input into a function.

For cos(x), x can be any real value (this is true because angles can go around and around and even land on top of each other, for example a rotation of 50 degrees and a rotation of 410 degrees lands at the same angle from the positive x-axis).   So, cos(x) domain is unrestricted.
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For arccos(x), there is a restriction that {{{ -1 <= x <= 1}}} because "cos(x)" always produces a number between -1 and +1 inclusive.  Thus, arccos() domain is restricted.
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So answer C looks right.