Ethylene oxide is treated with $\mathrm{CH}{}_3\mathrm{MgBr}$ in dry ether and the mixture is then worked up with dilute acid. The product is

The Grignard reagent acts as a carbon nucleophile and opens the strained ring by SN2 attack at a ring carbon. This adds $\mathrm{CH}{}_3$ to $\mathrm{CH}{}_2$ and leaves an alkoxide on the other $\mathrm{CH}{}_2$. Protonation gives $\mathrm{CH}{}_3\mathrm{CH}{}_2\mathrm{CH}{}_2\mathrm{OH}$, propan-1-ol.