Which compound is an aldehyde?

[Step 1]:Option (1) CH3−CH2−O−CH3 is an ether[Step 2]:Option (2) CH3−CH2−O−H  is an alcohol[Step 3]:Option (3) CH3−CH2−C||O−H  is an aldehyde[Step 4]:Option (4) CH3−CH2−C||O−CH3  is a ketone