When the argument of the secant function is changed from x to 2x+π, what happens to the set of x-values where the function is undefined?
a) They are compressed horizontally by a factor of 21 and shifted 4π units to the left.
b) They are compressed horizontally by a factor of 21 with no horizontal shift.
c) They are compressed horizontally by a factor of 21 and shifted 2π units to the left.
d) They are stretched horizontally by a factor of 2 and shifted 4π units to the right.