题目

 We should all remember that some great scientific discoveries _____________ by chance.    A. gained           B. discovered           C. occurred            D. earned 答案：C4．下列各式中，正确的是（　　）A．-（-1）＜-（+2）B．-$\frac{5}{6}＞-\frac{5}{7}$C．-（-5$\frac{1}{2}$）＞|-5.5|D．-$\frac{7}{8}$$＜-\frac{6}{7}$