下列说法正确的是（ ）
A．镁原子的质子数大于镁离子的质子数
B．相对原子质量就是一个原子的实际质量
C．任何原子中：质子数=中子数=电子数
D．由离子构成的物质一定含有阴离子和阳离子，但一定显中性
A、根据元素的种类由质子数决定，镁原子和镁离子属于镁元素的两种微粒，属于同种元素，故A说法错误；
B、相对原子质量：以一种碳原子（碳-12）质量的
作为标准，其他原子的质量跟它相比较所得的数值，因此相对原子质量就不是一个原子的实际质量；故B说法错误；1 12
C、根据在原子中，原子序数=质子数=核电荷数=核外电子数，故C说法错误；
D、由离子构成的物质含有阴离子和阳离子，它们所带电荷数相等，电性相反，所以由离子构成的物质一定显中性；故D说法正确；
故选D．
| Questions 91-95 are based on the following passage. It is amazing how many people still say, "I never dream", for it is now decades since it was established that everyone has over a thousand dreams a year, however few of these nocturnal productions are remembered on waking. Even the most confined "non-dreamers" will remember dreams if woken up systematically during the Rapid Eye Movement (REM) periods. These are periods of light sleep during which the eyeballs move rapidly back and forth under the closed lids and the brain becomes highly activated, which happens three or four times every night of normal sleep. It is a very interesting question why some people remember dreams regularly—perhaps several a night on occasion—while others remember hardly any at all under normal conditions. In considering this, it is important to bear in mind that the dream tends to be an elusive phenomenon for all of us. We normally never recall a dream unless we awaken directly from it, and even then it has a tendency to fade quickly into oblivion. Given this general elusiveness of dreams, the basic factor that seems to determine whether a person remembers them or not is the same as that which determines all other memory, namely degree of interest. Dream researchers have made a broad classification of people into "recallers" —those who remember at least one dream a month—and "non-recallers", who remember fewer than this. Tests have shown that cool, analytical people with a very rational approach to their feelings tend to recall fewer dreams than those whose attitude to life is open and flexible. Engineers generally recall fewer dreams than artists. It is not surprising to discover that in western society, women normally recall more dreams than men, since women are traditionally allowed an instinctive, feeling approach to life. In modern urban-industrial culture, feeling and dreams tend to be treated as frivolities which must be firmly subordinated to the realities of life. We pay lip-service to the inner life of imagination as it expresses itself in the arts, but in practice relegate music, poetry, drama and painting to the level of spare-time activities, valued mainly for the extent to which they refresh us for a return to work. We discourage our children from paying much attention to anything that might detract from the serious business of studying for exams or making a living in the "real" world of industry and commerce. |
Those who recall their dreams tend to be ______.
A．practical
B．unrealistic
C．disorganized
D．imaginative