18. In a track and field meet, 216 athletes participate in the 100-meter dash. The venue has 6 lanes, with 1 athlete in each lane. Each race has 6 participants, and only the first-place finisher in each group advances to the next round. It will take ( ) races to determine the champion.
(A) 36
(B) 42
(C) 43
(D) 60
(E) 72
18. C.

In the first round, $\frac{1}{6}$ of the total number, which is $\frac{216}{6}=36$ players, advance to the second round, with a total of 36 matches played; in the second round, $\frac{36}{6}=6$ players advance to the final, with 6 matches played; in the third round, only 1 match is played to determine the champion. Therefore, a total of $36+6+1=43$ matches are played.