The policemen set him free when his ransom had not yet been paid.他还未交赎金，警察就把他放了。 Obviously, there would be no point in investing in a computer if you had to check all its answers, but people should also rely on their own internal computers and check the machine when they have the feeling that something has gone wrong.显然，如果计算机给出的全部答案均需要核查，花钱买计算机就毫无意义。不过，人们也应该信赖自身内部的计算能力，在认为计算机有问题时进行复查。