Which of the following statements is true?

A: The number of electron shells in an atom is called the atomic number.
B: Boiling and melting points are chemical properties.
C: A molecule of oxygen can have atoms of carbon in it.
D: Elements are substances made of only one type of atom.

Select the correct answer. which mutation is harmful to the organism? a. a mutation allowing moths to camouflage better on blackened tree bark b. a mutation making staphylococcus aureus resistant to the antibiotic methicillin c. a mutation inhibiting human immunodeficiency virus from attaching to and entering the cell d. a mutation causing uncontrolled cell division e. a mutation giving plant leaves a bitter taste to discourage herbivores from eating them