The given series of reactions proceed as follows:

CH3OH (methanol) is oxidized to HCOH (formaldehyde).HCOH is further oxidized to HCOOH (formic acid).HCOOH reacts with CH3OH to form HCOOCH3 (methyl formate).HCOOCH3 undergoes a decarboxylation reaction to form CO2.Finally, CO2 can react with CaO to form CaCO3 (calcium carbonate).

Therefore, the correct sequence of reactions is as follows:
CH3OH → HCOH → HCOOH → HCOOCH3 → CO2 → CaCO3