Example 1 Given a linear function $y=kx+b, kb<0$. Then the graph of such a linear function must pass through $\qquad$ quadrants, i.e., the $\qquad$ quadrant.
(14th Junior High School Mathematics Competition in Jiangsu Province)
Solution: When $k b0, b0$, its graph passes through the first, second, and fourth quadrants.

Therefore, the graph of this linear function must pass through two common quadrants, namely the first and fourth quadrants.