Grocery store price lists are updated by______.

A．Migration of large numbers of people may cause conflict.
B．The newest arrivals can hardly get good jobs.
C．Native people often resent newest arrivals because they cannot communicate easily with the latter.
D．Usually it has taken several decades for each group of newest arrivals to be accepted into the mainstream of society in the host country.

A．the human voices in commercials have more auditory impact
B．people like cheerful songs that change dramatically in sound quality
C．high-frequency sounds are used to mask sounds that drown out the primary message
D．they possess sound qualities that make the viewer feel that something unusual is happening