Which of these happened in Precambrian time? A. The first mammals appeared.
B. Life began to evolve on Earth.
C. A mass extinction wiped out most dinosaurs.
D. Life on Earth began to move from water to land

Select the correct answer from each drop-down menu. a system of equations and its solution are given below. system a complete the sentences to explain what steps were followed to obtain the system of equations below. system b to get system b, the equation in system a was replaced by the sum of that equation and times the equation. the solution to system b the same as the solution to system a.]