Question

multiple choice question
it was difficult to find evidence for the existence of a sixth quark because
o high - speed collisions never result in the release of the sixth quark
o only about one - billionth of a percent of collisions studied showed its presence
o scientists needed to come up with a completely different method to detect it

Explanation:

Quarks are sub - atomic particles. The sixth quark was hard to detect because its presence was extremely rare in the studied collisions. Only about one - billionth of a percent of collisions showed its presence, making evidence collection difficult.

Answer:

only about one - billionth of a percent of collisions studied showed its presence