A.adenine B.thymine C.cytosine D.uracil E.guanine 18. Which of the following are paired bases in DNA? 21. In the model of DNA, the “rungs” of the ladder are composed of: A.sugars B.paired bases C.phosphates D.a sugar and a phosphate molecule 22. If 30% of an organism”s DNA is thymine, then: A.70% is deoxyribose B.20% is guanine C.20% is adenine D.40% is guanine 23. In a DNA molecule, the: A.backbone is composed of covalently bonded bases B.sugars are composed of 8 carbon rings C.bases are hydrogen bonded to one another D.adenine and cytosine base pair to each other 24. Which of the following contains thymine? A.DNA B.mRNA C.rRNA D.protein E.tRNA 25. In DNA, what makes up the “sides” of the ladder? A.It forms a double helix. 26. Which of the following is NOT true about DNA?