问题
单项选择题
不同历元不同测站同步观测同组卫星的三差可消除（）影响。
A.卫星钟差
B.接收机钟差
C.整周未知数
D.大气折射
答案
参考答案：C
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不同历元不同测站同步观测同组卫星的三差可消除（）影响。
A.卫星钟差
B.接收机钟差
C.整周未知数
D.大气折射
参考答案：C
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| Every country has its own dining customs. Americans feel that the first rule of being a 1 guest is to be on time. If a person is invited to dinner at six thirty, the hostess 2 him to be there at six thirty or 3 a few minutes after. Because she usually does the cooking, she has to time the meal 4 the hot rolls and the coffee and the meat can be at their best when the guests come. If they are late, the food will not be so 5 , and the hostess will be 6 . 7 the guest cannot come on time, he should call his host or hostess on the phone, give the reason, and tell 8 what time he can come. 9 the situations, guests sometimes bring a box of candy, a bottle of wine or a bunch of flowers to give to the hostess as a 10 of appreciation. As guests continue to arrive, it is usually considered polite for the 11 in the group to 12 when a woman enters the room and continue to stand until she is seated. 13 , most young people and some groups of elder people 14 stress equality of the sexes no longer observe the custom. A visitor should be 15 to each situation and follow the lead of the Americans present. When the guests sit down at a dinner table, it is a 16 for the men to help the ladies by pushing their chairs under them. However, some Americans 17 do this, so the visitors must notice what others do and do the 18 . 19 the meal is under way and if the dinner is in a private home, a guest 20 avoid embarrassment by leaving talk to someone else. | |||
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