Which of the following is NOT true of isotherms:

W) they are more widely spaced over the equatorial regions

X) they are more closely spaced over North America in the summer than in the winter

Y) they tend to be linear in form in the Southern Hemisphere south of 40\({}^{\rm o}\) latitude

Z) they are lines that connect places with the same average temperature
X) THEY ARE MORE CLOSELY SPACED OVER NORTH AMERICA IN THE SUMMER THAN IN THE WINTER