(1) Scholars are limited in charting the details of early human social evolution because of the loss of evidence from natural causes. (2) But owing to the fortunate "airtight" atmospheric conditions in numerous caves of France and Spain, we know that between 33,000 and 12,000 years ago, humans produced some of the most stunning paintings in the entire history of human art. (3) In more than two hundred caves so far discovered (some as recently as 1991 and 1994), the earliest known artists painted breathtaking murals of prancing animals—bison, bulls, horses, stags, and even rhinoceroses. (4) The emphasis in this cave art was on movement. (5) Almost all of the murals depict game species running, leaping, chewing their cud, or facing the hunter at bay. (6) An ingenious device for giving the impression of motion was the drawing of additional outlines to indicate the areas in which the leg or the head of the animal had moved. (7) The cave painters sometimes achieved startling three-dimensional effects by using the natural bumps and indentations of the cave surfaces. (8) All in all, visitors today who are lucky enough to see the cave murals usually find them as stimulating as any paintings hanging in the world's foremost art museums.
A2. The author implies that
a. artists have learned little throughout the centuries.

b. the cave artists were creative and talented.

c. the cave artwork was done quickly.

d. at the time of the cave painters, interest in art was unusual.