Complete the sentences to describe the structure of DNA. The shape of the DNA molecule is called a double . The backbone of DNA is made of molecules and phosphate molecules. The "rungs" of DNA are made of .

Witch layer of the atmosphere has the most air pressure

Why is the study of demography important to geographers

Which of the following best describes the purpose of a nation’s boundaries? a. to limit the movement of goods and people b. to make it easier for cartographers to create maps c. to make the movement of goods and people easier d. to prevent other countries from invading territory