\(\mathop {\lim }\limits_{x \to 0} \frac{{\cos ax - \cos bx}}{{{x^2}}}\)
A.\(\frac{a^{2} - b^{2}}{2}\)
B.\(\frac{a^{2} + b^{2}}{2}\)
C.\( a^{2} - b^{2}\)
D.\(\frac{b^{2} - a^{2}}{2}\)

\(\mathop {\lim }\limits_{x \to 0} \frac{{\sin 6x + \sin 4x}}{{\sin 3x + \sin 5x}}\)
A.\(1\)
B.\(\frac{4}{3}\)
C.\(\frac{1}{2}\)
D.\(\frac{5}{4}\)

\(\mathop {\lim }\limits_{x \to 0} \frac{{1 - \sin 2x - \cos 2x}}{{1 - \sin 2x + \cos 2x}}\)
A.\(1\)
B.\( - 1\)
C.\(0\)
D.\(\frac{1}{2}\)

\(\mathop {\lim }\limits_{x \to a} \frac{{{{\sin }^2}x - {{\sin }^2}a}}{{{x^2} - {a^2}}}\)
A.\(\frac{\sin {a}}{a}\)
B.\(\frac{\sin {2a}}{2a}\)
C.\(\frac{\cos {a}}{a}\)
D.\(\frac{\cos {2a}}{2a}\)

\(\mathop {\lim }\limits_{x \to \frac{\pi }{4}} \frac{{\sin \left( {\frac{\pi }{4} - x} \right)}}{{1 - \sqrt 2 \sin x}}\)
A.\(1\)
B.\(\frac{1}{2}\)
C.\(2\)
D.\( - 1\)

\(\mathop {\lim }\limits_{x \to \frac{\pi }{6}} \frac{{2\sin x - 1}}{{4{{\cos }^2}x - 3}}\)
A.\( - \frac{3}{2}\)
B.\( - \frac{1}{4}\)
C.\(\frac{1}{2}\)
D.\( - \frac{1}{2}\)

\(\mathop {\lim }\limits_{x \to \frac{\pi }{6}} \frac{{2\sin x - 1}}{{4{{\cos }^2}x - 3}}\)
A.\( - \frac{3}{2}\)
B.\( - \frac{1}{4}\)
C.\(\frac{1}{2}\)
D.\( - \frac{1}{2}\)

\(\mathop {\lim }\limits_{x \to b} \frac{{\cos x - \cos b}}{{x - b}}\)
A.\(\sin b\)
B.\( - \cos b\)
C.\( - \sin b\)
D.\(\cos b\)

\(\mathop {\lim }\limits_{x \to a} \frac{{{{\sin }^2}x - {{\sin }^2}a}}{{{x^2} - {a^2}}}\)
A.\(\frac{\sin {a}}{a}\)
B.\(\frac{\sin {2a}}{2a}\)
C.\(\frac{\cos {a}}{a}\)
D.\(\frac{\cos {2a}}{2a}\)

Trong Đông - Xuân 1953 - 1954, quân dân Việt Nam đã làm phá sản bước đầu kế hoạch quân sự nào của thực dân Pháp?
A.Kế hoạch Đácgiăngliơ.
B.Kế hoạch Nava.
C.Kế hoạch Bôlae.
D.Kế hoạch Rơve.