18. Six bags contain 18, 19, 21, 23, 25, and 34 glass balls respectively, one of which contains only balls with cracks, while the other five bags contain no such cracked balls. Jenny took three of the bags, and George took two of the bags, leaving only the bag with the cracked balls. If Jenny got exactly twice as many balls as George, how many balls with cracks are there?
(A) 18;
(B) 19;
(C) 21;
(D) 23; (E) 25.
18. Jenny has twice as many balls as George, so the total number of balls they take must be a multiple of 3. This indicates that the difference between 140 (18 $+19+21+23+25+34=140$ ) and the number of balls with cracks must be a multiple of 3. It is easy to verify that among the six given bags of balls, only $140-23$ is a multiple of 3, so the number of balls with cracks is 23.
(D) True.