List two important groups of organisms that appeared during each of the three most recent geologic eras

Suppose that a comet that was seen in 563 a.d. by chinese astronomers was spotted again in year 1951. assume the time between observations is the period of the comet and take its eccentricity as 0.986. what are (a) the semimajor axis of the comet's orbit and (b) its greatest distance from the sun?

Which lists the organs in the correct order as food passes from the mouth to anus?

Which is the correct symbol for an isotope of iodine with 53 protons and 78 neutrons?