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【简答题】
在数列{a n }中，如果对任意的n∈N * ， a n+2 a n+1 - a n+1 a n =λ （λ为常数），则称数列{a n }为比等差数列，λ称为比公差．现给出以下命题： ①若数列{F n }满足F 1 =1，F 2 =1，F n =F n-1 +F n-2 （n≥3），则该数列不是比等差数列； ②若数列{a n }满足 a n =(n-1)? 2 n-1 ，则数列{a n }是比等差数列，且比公差λ=2； ③等比数列一定是比等差数列，等差数列不一定是比等差数列； ④若{a n }是等差数列，{b n }是等比数列，则数列{a n b n }是比等差数列． 其中所有真命题的序号是______．
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【单选题】--Recent years have______rapid changes of my hometown. --Yes, I could hardly recognize it when I arrived yesterday,
A.
watched
B.
witnessed
C.
contributed
D.
made
【单选题】When she (arrived), I was (pretty) fed up, because I (waited) (since) eight o'clock.
A.
arrived
B.
pretty
C.
waited
D.
since
【单选题】Hello! I'm glad to see you here. When _____ you _____? [ ]
A.
did, arrive
B.
will arrive
C.
have, arrived
D.
are arriving
【单选题】—I’m going to attend your lecture at 9∶30 tomorrow morning. —I regret to tell you that. When you arrive, it will have ended and I ________ questions with my students.
A.
would discuss
B.
will discuss
C.
will be discussing
D.
am discussing
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