In the following diagram, four different index fossils are labeled: which of the labeled fossils comes from the youngest organism? a b c d

If you look at the leftmost part of the graphic, it includes a time axis, where the top represents the most recent time and the bottom the earlier times, so just using this axis, we can see that the fossil A is the earliest, or the youngest, because it it the highest one. - This is the correct answer, fossil A. 

Additionally, we could look at the periods - our fossil A is from the Jurassic period. we can compare it to the fossil B, which is from Permian period. Indeed, Jurassic is a younger age than Permian (or  Devonian and Cambrian, the ages of C and D) - so this confirms that A is the best answer. 

Sequoia national park  /  inyo national forest, california, u.s. mount whitney is the tallest mountain in california, as well as the highest summit in the contiguous united states and thesierra nevada—with an elevation of 14,505 feet (4,421 m).