Given the age of the meteorite is 4.5 billion years old with 78 atoms of lead-206 the answer should be B. 156. The half-life of uranium-238 in order to decay into lead-206 is 4.46 billion years, which means that the original number of atoms is 156.
Cell transport is useful because it's, essentially, the movement of cells across the blood/veins. Active transport uses energy, while passive transport does not.
