How many different types of bases can be found on dna?

Which would prevent a plant from growing

Plz ! for many generations farmers in north america have been choosing to cross corn plants with large ears of corn each year this results in the new generation of plants also growing large ears of corn. what is the technique called? a. selective breeding. b. natural selection. c. mitosis. d. asexual budding.

What form of anesthetic was used for field surgery