A.5
B.6
C.7
D.4

A.Mg, Al2O3, Al.
B.Mg, K, Na.
C.Fe, Al2O3, Mg.
D.Zn, Al2O3, Al.

A.1,0.
B.1,2.
C.0,3.
D.0,8.

A.\({\log _a}\dfrac{1}{x} = \dfrac{1}{{{{\log }_a}x}}\)     
B.\({\log _a}\left( {xy} \right) = lo{g_a}x + {\log _a}y\)
C.\({\log _a}\dfrac{x}{y} = {\log _a}x - {\log _a}y\)   
D.\({\log _b}a.{\log _a}x = {\log _b}x\)

A.\(\ln x < 1 \Leftrightarrow 0 < x < 1\)   
B.\(\log a > \log b \Leftrightarrow a > b > 0\)
C.\(\ln x > 0 \Leftrightarrow x > 1\)     
D.\(\log a < \log b \Leftrightarrow 0 < a < b\)

A.\( - C_8^1{.2^3}\)  
B.\( - C_8^5{.2^5}\)   
C.\(C_8^3{.2^3}\)   
D.\(C_8^5{.2^5}\)

A.\(\dfrac{{21}}{{16}}\)   
B.\(\dfrac{{21\pi }}{{16}}\)   
C.\(\dfrac{{15}}{{16}}\)    
D.\(\dfrac{{15\pi }}{8}\)

A.6 lần  
B.36 lần   
C.12 lần   
D.18 lần

A.4 cạnh  
B.3 cạnh   
C.6 cạnh   
D.5 cạnh

A.\({\log _a}b\)  
B.\({\log _b}c\)   
C.\({\log _c}d\)   
D.\({\log _d}a\)