When an alkene undergoes ozonolysis, the double bond is cleaved, and the carbons involved in the double bond are converted to carbonyl groups (C=O). In this specific case, Alkene A, upon ozonolysis, yields ethanal (CH3CHO) and pentan-3-one (CH3CH2COCH2CH3). This indicates that the original alkene A contains a double bond connecting a two-carbon fragment (resulting in ethanal) and a five-carbon fragment with a carbonyl group at the 3rd carbon (resulting in pentan-3-one). Reconstructing the original alkene involves joining these two fragments at the carbonyl carbons, removing the oxygen atoms and forming a double bond in its place. Therefore, Alkene A is 3-ethyl-2-pentene or a structural isomer of it.