Fill in the blanks to make the following statements correct.
a. The allocation of different jobs to different people is referred to as the ________of labour. The specialization within the production process of a particular product is referred to as the________ of labour.
b. When people specialize in their activities, it becomes necessary for them to________ to obtain most of the things they need or want.
c. Trade is facilitated by _______ because it eliminates the cumbersome system of barter.
d. The rapid reduction in both transportation and communication costs has greatly contributed to the_________ of the world economy.