[填空题]Smog does great harm to the respiratory system.

[填空题]Smog does great harm to the respiratory system.

[填空题]Smoking does harm to us. Under no circumstances __________________________________ (公共场所禁止吸烟).

[填空题]The harm the electromagnetic radiation does to people’s health is as great as or even greater than that cigarette smoking does.

[单项选择]No one can be a great thinker who does not realize that as a thinker it is his first duty to follow his intellect to whatever conclusions it may lead. Truth gains more even by the errors of one who, with due study and preparation, thinks for himself, than by the true opinions of those who only hold them because they do not suffer themselves to think. Not that it is solely, or chiefly, to form great thinkers that freedom of thinking is required. On the contrary, it is as much or even more indispensable to enable average human beings to attain the mental quality which they are capable of. There have been, and may again be, great individual thinkers in a general atmosphere of mental slavery. But there never has been, nor ever will be, in that atmosphere an intellectually active people. While any people has made a temporary approach to such a character, it has been because the dread of heterodox(非正统的) thinking was for a time suspended. Where there is an unspoken convention that principles
A. even persons are promoted to thinking beings.
B. big and vital issues are freely and widely discussed.
C. great thinkers have emerged from the ordinary intellects.
D. people become enthusiastic about thinking independently.