Which statement best describes how Watson and Crick's model used other scientists' work to create a model of DNA? They used Chargaff's rule to determine that it contains ribose sugar.
They used Franklin's photo to determine that DNA was a double helix.
They used Levene's work to determine the number of base pairs in each strand.
They used Nirenberg and Matthei's studies to determine that DNA is made of nucleotides.

Which of the following describes a negative feedback loop? when the heart rate is too high, the body sends hormones that continually increase the heart rate higher. when a pregnant woman is in labor, the body sends hormones that increase the intensity of contractions, which then increases the secretion of the same hormones. when blood sugar is too low, the body sends hormones that raise blood sugar until it reaches a typical level and hormone secretion slows. when a person is jogging, the body sends hormones that continually decrease the rate of oxygen supply to the legs.