"the sports gene": which detail most strongly supports the idea that a longer
achilles tendon might lead a person to have greater high-jumping abilities?
a) kangaroos have longer tendons that lead them to bouncing instead of
walking.
b) donald thomas had his long achilles tendons studied by a neuromuscular
scientist.
c) donald thomas has not improved his high-jumping after doing it for six years.
neither ishikawa nor hunter think that the sole secret of a person's jumping
success is in their achilles tendons.

The statement which best supports the idea that a longer Achilles tendon might lead a person to have greater high-jumping abilities is that kangaroos have longer tendons that lead them to bouncing instead of walking (a).

Not only do the other statements (b and c) go against this claim, but the first one directly expresses a causation. Indeed, through the use of the verb lead to, this sentence affirms that the fact that kangaroos have longer tendons than other bipeds is the reason why they are able to jump instead of simply walking.