Which of the following is an uncountable noun?
Let's consider b., c., and d.
b. You can certainly count the amount of friends you have.
"I have three close friends, and ten other friends with whom I'm not so close."
"My four grade school friends and I got together the other night for the sake of reflecting on old times."
c. One can definitely have multiple peanuts and show how many peanuts there are by counting. On its own, "peanut" is a singular noun, referring to just a single peanut.
"There are three peanuts left in that bag."
"Each container of our peanut butter is made from fifty fresh peanuts!"
d. As a noun, "baby" refers to a single young infant. Babies are absolutely countable.
"The hospital's maternal ward can hold up to twenty babies at a time."
"Mrs. Smith gave birth to two beatiful baby boys last week. I wish her the best in her journey as a mother!"
Now, regarding a.:
An education is a systematic instruction, namely at a school or university. One can be college-educated, primary school-educated, or uneducated; however, one cannot be two-educated, three-educated, or four-educated. Education cannot be counted with numbers, but it can be classified, such as college education, graduate school education, or high school education.