Which of these is a characteristic of cool air? a. it rises through the lower atmosphere. b. it is found close to earth's surface. c. it sinks due to convection. d. it moves through radiation.

The correct option is C.
There are three major means by which heat is transfers from one object to another, these are: conduction, convection and radiation. Convection is the process by which heat is transfer from one place to another through movement of fluids. When air is heated, it becomes warm, lighter and  gains more kinetic energy, therefore it rises and move away from the heat source, as it does this, it loses heat and cools down. The cooled air becomes heavier and sinks backs towards the heat source. This cycle is continuous and it sets up a convection current.

The basic repeating unit of nucleic acids are known as nucleotides. a nucleotide consists of three distinct chemical groups.

The soviet union beat the us to the first successful launch, with the october 4, 1957, orbiting of sputnik 1, and later beat the us to have the first human in earth orbit, yuri gagarin, on april 12, 1961. the "race" peaked with the july 20, 1969, us landing of the first humans on the moon with apollo 11