In the 1960s and 1970s, the united states fought a war in vietnam in order to
a. acquire more land for the u. s.
b. get revenge after being attacked.
c. defend its european allies.
d. stop the spread of communism.

What was piaget's explanation as to why preschool-age children in the preoperational stage make errors on tasks requiring conservation? a) preschool children's tendency toward centration prevents them from focusing on other relevant features of a situation b) preschool children have not yet developed numerical understanding; therefore, different amounts are meaningless c) preschool children's neural-visual network is not fully matured d) preschool children have not lived long enough and accrued enough experience to know the difference between quantities