Phương trình $\sin x+\sin 2x+\sin 3x=\cos x+\cos 2x+\cos 3x$ có tập nghiệm trùng với tập nghiệm của phương trình nào sau đây?
A. $\sin x=-\frac{\sqrt{3}}{2}$ 
B. $\cos 2x=\sin 2x$ 
C. $\cos x=\frac{1}{2}$ 
D. $\left[ \begin{array}{l}\cos x=-\frac{1}{2}\\\cos 2x=\sin 2x\end{array} \right.$

 Trong các hàm số sau, hàm số chẵn là
A. $y=-\sin x.$
B. $y=\cos x-\sin x.$
C. $y=\sin x.cosx.$
D. $y=\cos x+{{\sin }^{2}}x.$

Phương trình $\frac{\sin 2x}{\tan x-1}=0$ có nghiệm là
A. $x=k\frac{\pi }{2},k\in Z.$
B. $x=k\pi ,k\in Z.$
C. $x=\frac{\pi }{3}+k2\pi ,k\in Z.$
D. Vô nghiệm.

Nghiệm của pt $\tan x+\cot x=2$ là 
A. $x=-\frac{\pi }{4}+k\pi $ 
B. $x=\frac{\pi }{4}+k\pi $ 
C. $x=\frac{5\pi }{4}+k2\pi $ 
D. $x=-\frac{3\pi }{4}+k2\pi $

Choose the best answer for the following sentence:
_________ she agreed, you would have done it.  
A. If                
B. Had                     
C. Should                 
D. Would

Choose the best answer for the following sentence:
I write letters ___________ my left hand. 
A. in                
B. by                  
C. with                     
D. at

Choose the best answer for the following sentence:
She ___________ a pair of shoes from among the dozen the salesgirl'd shown he 
A. picked                 
B. selected                   
C. opted                  
D. sorted

Choose the best answer for the following sentence:
Some of the proposals ___________ . 
A. were strongly objected                    
B. strongly objected to
C. were strongly objected to                 
D. strongly objected

Choose the best answer for the following sentence:
My brother _______ his job last month and since then he _____ out of work.
A. lost - has been
B. has lost - was
C. was losing - has been
D. was loosing - was

Choose the best answer for the following sentence:
We would like to thank the local enterprises we work _______________ to organize the event.
A. on cooperation with
B. on cooperation of
C. in cooperation with
D. in cooperation to