Here's why:

* RNA uses uracil (U) instead of thymine. Uracil pairs with adenine (A) in RNA, just like thymine pairs with adenine in DNA.

* DNA uses thymine (T) instead of uracil.

So, the four bases found in RNA are:

* Adenine (A)

* Guanine (G)

* Cytosine (C)

* Uracil (U)