Game

A swim team with exactly five members -Jacobson,Kruger,Lu,Miller,Ortiz-swims a ten-lap relay race. Each team member swims exactly two of the laps: one swims laps 1 and 6, one swims laps 2 and 7, one swims laps 3 and 8, one swims laps 4 and 9, and one swims laps 5 and 10. The following conditions apply:

Neither of Kruger's laps is immediately before either of Lu's
Jacobson does not swim lap 9.
Ortiz's first lap is after (but not necessarily immediately after) Miller's.
At least one of Jacobson's laps is immediately after one of Ortiz's laps.

20. If Jacobson swims lap 8, then for exactly how many of the ten laps can one determine which team member swims the lap?

(A) ten
(B) eight
(C) six
(D) four
(E) two

搞不懂它到底在问什么? 是有哪几个 laps  可以被决定?