48.______ much is known about what occurs during sleep, the precise function of sleep and its different stages remains
    largely in the realm of assumption.
    A) Because B) For C) Since D) While
    49.John doesn’t believe in ______ medicine; he has some remedies of his own .
    A) standard B) regular
    C) routine D) conventional
    50.Owing to ________ competition among the airlines, travel expense have been reduced considerably.
    A) fierce B) strained
    C) eager D) critical
    51.They always give the vacant seats to comes first.
    A) whoever B) whomever
    C) who D) whom
    52.In Africa, educational costs are very low for those who are _________ enough to get into universities.
    A) ambitious B) fortuante
    C) aggressive D) substantial
    53.Professor Wang,_______ for his informative lectures, was warmly receive d by his students.
    A) knowing B) to be known
    C) known D) having known
    54.Our manager is _______ an important customer now and he will be back this afternoon.
    A) calling on B) calling up
    C) calling in D) calling for
    55.A fire engine must have priority as it usually has to deal with some kind of _______ .
    A) precaution B) crisis
    C) emergency D) urgency
    56.He said that the driver must have had an accident; otherwise he _____ by then.
    A) would have arrived B) should arrive
    C) must have arrived D) would arrive
    57.The film provides a deep _______ into a wide range of human qualities and feelings.
    A) insight B) fancy
    C) imagination D) outlook
    58.It is high time that such practices __________ .
    A) are ended B) be ended
    C) were ended D) must be ended
    59.Urban crowdedness would be greatly relieved if only the _____ charged o n public transport were more reasonable.
    A) fees B) payments C) fares D) costs
    60.The doctor had almost lost hope at one point, but the patient finally _________ .
    A) pulled out B) pulled up
    C) pulled through D) pulled over