Can a purine pair with a purine?

A always pairs with T and C always pairs with G. A and G are purines, meaning that they have two rings, while T and C are pyrimidines, meaning they have one ring.  Due to the Watson and Crick model, the width of DNA is constant, meaning that there must be a consistant width in each base pairing.  As a result, only a purine can pair with a pyrimidine, giving each base pairing a total of 3 rings.

Explanation:

events in order:

1.       vishnu schist

2. zoroaster granite

3. bass limestone

4. hakatar   shale

5. igneous intrusion

6. shinumo quartzite

7. dox sandstone

8. tapeats limestone

9. bright angel shale

10. muav limestone

11. temple butte limestone

12. redwall limestone  

nonconformity

answer: the unkar group shows angular unconformity because the layers are turned at angle.

unconformity

answer: specifically the angular unconformity occurs between the cambrian and precambrian rocks. the dox sandstone, shinumo quartzite, hakatar shale, and bass limestone have been filled. an angular unconformity occurs between the cambrian and precambrian rocks. the dox sandstone, shinumo quartzite, hakatar shale, and bass limestone have been filled.

disconformity

answer: the disconformities aremarked irregular lines between the sedimentaryrocks layers.

the correct answer is d