x，y互为相反数，则x+y=0．
a，b互为倒数，则ab=1．
则（x+y）-4ab=-4．
No one could recognize me after I got my new transistors in the 31 (1960).There were times when my size was 32 (total) changed. I became small and thin but I got cleverer and cleverer, quicker and quicker. And my memory became so large 33 I couldn’t believe it! But I was always so lonely 34 (stand) there by myself, 35 in the early 1960s, they gave me a family 36 (connect) by a network. I could share information 37 others and we could talk to each other. At about the same time we learned to talk to humans using BASIC. I was brought into people’s homes in the 1970s. Since then, my family and I 38 (use) by 39 (billion) of people to deal with information and communicate with each other around the world by the Internet. I love 40 (use) to connect people who aren’t close enough to speak to each other. I have truly been built to serve the human race since my birth.
用高压锅煮饭，熄火后用冷水将锅冷却，拿去限压阀后打开锅盖，可以看到锅内的粥仍在沸腾，而普通的铝锅却看不到这种现象。这是因为：
A．熄火后，锅内的温度迅速降到100%：以下，但由于打开锅盖后气压降低，所以粥会重新沸腾
B．粥的流动性差，不易降温，熄火后即使不浇冷水，不拿去限压阀，粥也要沸腾较长时间
C．熄火后，锅内的温度仍然高于100℃，即使不冷却，不拿去限压阀，粥也会在沸腾
D．熄火后，锅内的温度仍然高于100℃，冷却后锅内气压比原来降低，所以粥会重新沸腾
