[单项选择]下列关于要约的表述中，正确的是( )。
A. 要约在发出时生效
B. 要约在到达受要约人时生效
C. 要约生效后不得撤销
D. 只要受要约人未发出承诺通知，要约均可撤销

下列说法何者不正确？（）
Ⅰ、除《国际海上避碰规则》第二章第一节和第二节另有规定外，追越船应给被追越船让路
Ⅱ、任何情况下，只要一船从另一船的正横后大于22.5度方向上赶上他船，就必须给他船让路
Ⅲ、不论《国际海上避碰规则》第二章第二节和第三节如何规定，追越船均应给被追越船让路

All of us communicate with one another nonverbally, as well as with words. Most of the time we’re not aware that we’re doing it. We gesture with eyebrows or a hand, meet someone else’s eyes and look away, shift positions in a chair. These actions we assume are random(随意的) and incidental. But researchers have discovered in recent years that there is a system to them almost as consistent and comprehensible (可充分了解的) as language.
Every culture has its own body language, and children understand its meanings along with spoken language. A Frenchman talks and moves in French. The way an Englishman crossed his legs is nothing like the way a male American does it. In talking, Americans are apt to end a statement with a droop(垂下) of the head or hand, a lowering of the eyelids(眼皮). They wind up(结束)a question with a lift of the hand, a tilt(倾斜) of the chin or a widening of the eyes. With a future-tense verb they often gesture with a forward movement.

A. Sex and ethnic background.
B. Social class and personal style.
C. Body language.
D. None of the above.