Which of the following is a synthesis reaction?

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1

Which of the following is a synthesis reaction?
A) 2H2 + O2 → 2H2O.
B) 2H2O2 → 2H2O + O2.
C) CaCO3 → CaO + CO2.
D) 2AgNO3 + Zn → 2Ag + Zn(NO3)3