Which of the following is TRUE according to the passage

A．Birds evolved from reptiles.
B．It is known to all that flight developed when a ground-living form began to flap its wings to increase its running speed.
C．It is known to all that flight developed when a tree-climbing form used imperfect wings to aid it in leaping from tree limb to tree limb.
D．The evolution from reptile to the bird concluded about 75 thousand years ago.