Choose the best answer for the following sentence:
The doctor persuaded the patient ______________________ in hospital for 3 more days. 
A. staying                
B. to stay                   
C. being stayed                  
D. stay

Choose the best answer for the following sentence:
“I don’t know whether to take that mathematics course or not.” “If ___________ you, I’d take it.” 
A. I am               
B. I will be                
C. I had been                 
D. I were

Choose the best answer for the following sentence:
One of our difficulties is we do not always have the ____________ addresses of all our members. 
A. up to date                     
B. to update
C. up-to-date                   
D. up to-date

Choose the best answer for the following sentence:
She has a lot to be thankful for; but _________ thing of all is that she does not realize it. 
A. the sadder                         
B. sadder
C. the saddest                   
D. saddest

Choose the best answer for the following sentence:
Scientists recognize that species continually disappear at a background _____________ rate estimated at about one species per million per year, with new species replacing the lost in a sustainable fashion. 
A. extinct                    
B. extinction                   
C. extinctivity                 
D. extinctiveness

Choose the best answer for the following sentence:
Why did you leave so hurriedly?
If you __________ there for another week, he __________ your portrait. 
A. had stayed - would finish                   
B. had stayed - would have finished
C. stayed - would have finished                 
D. would have stayed - would have finished

Choose the best answer for the following sentence:
I'm sure it's not my fault that Peter found out what we were planning. I don'tremember ___________________ anyone about it.
A. having told              
B. being told                 
C. to tell                  
D. to be told

Cho dãy só với u1=2un+1=2.un
Khảng định đúng là
A. Công thức số hạng tổng quát của dãy số : un = nn-1.
B. Công thức số hạng tổng quát cuản dãy số un=2n.
C. Công thức số hạng tổng quát cuản dãy số un=2n+1.
D. Công thức số hạng tổng quát cuản dãy số un=2.

Cấp số nhân trong các dãy số sau là
A. u1=12un+1=un.
B. u1=12un+1=-2.un.
C. un=n2+1.
D. u1=1; u2=2un+1=un+1.un.

Số hạng lớn nhất của dãy:   là
A. .
B. 1.
C. .
D. .