Rock Layer B is about 1408 million years old. How much of the original uranium-235 would you expect to find in the sample?

Yes, you can get ap exam prep books that correspond to the exam you will be taking. i honestly think the ap biology exam was one of the easier exams to take.

Psychologists often talk of the magical number "7" - so it is generally assumed that we can keep 7 (more or less, so 5-9 is the correct answer) items in our short term memory - we know this as a result of many experiments.

we can increase this by chunking, so for example "7 8 9 5 3" is harder to remember than "78 95 3" - try it yourself!

the answer is a)