A.CaCO3 → CaO  + CO2.
B.Ca(OH)2 + Na2CO3 → CaCO3 + 2NaOH.
C.Ca(HCO3)2 → CaCO3 + CO2 + H2O.
D.CaCO3 + CO2 + H2O → Ca(HCO3)2.

A.Fe(NO3)3.
B.FeNO3.
C.Fe(NO3)2 và Fe(NO3)3.
D.Fe(NO3)2.

A.Cu.
B.Na.
C.Al.
D.K.

A.\( - 4\)
B.\( - 2\)
C.\( - 3\)
D.\( - 5\)

A.\(u = 40co{\rm{s}}\left( {100\pi t + \frac{\pi }{4}} \right)\left( V \right)\)
B.\(u = 40co{\rm{s}}\left( {100\pi t - \frac{\pi }{4}} \right)\left( V \right)\)
C.\(u = 40\sqrt 2 co{\rm{s}}\left( {100\pi t - \frac{\pi }{4}} \right)\left( V \right)\)
D.\(u = 40\sqrt 2 co{\rm{s}}\left( {100\pi t + \frac{\pi }{4}} \right)\left( V \right)\)

A.\(z = 4 + 3i\)
B.\(z = 3 - 4i\)
C.\(z = 3 + 4i\)
D.\(z =  - 3 + 4i\)

A.\(12 + 5i\)
B.\( - 12 + 5i\)
C.\(12 - 5i\)
D.\( - 12 + 8i\)

A.\(r = 2\)
B.\(r = 2\sqrt 2 \)
C.\(r = 4\)
D.\(r = 3\sqrt 2 \)

A.\(G\left( {\frac{1}{3}; - 1;\frac{5}{3}} \right)\)
B.\(G\left( {\frac{1}{2}; - \frac{3}{2};\frac{5}{2}} \right)\)
C.\(G\left( {1; - 3;5} \right)\)
D.\(G\left( {\frac{5}{3};0;\frac{1}{3}} \right)\)

A.\(\frac{{2x}}{{{x^2} + 2}}\)
B.\(\frac{1}{{{x^2} + 2}}\)
C.\(\frac{x}{{{x^2} + 2}}\)
D.\(2x\left( {{x^2} + 2} \right)\)