Which of the following ethers give $(\mathrm{CH}{}_3){}_3\mathrm{C}-\mathrm{I}$ as one product when treated with one equivalent of HI at room temperature (SN1 cleavage at the tertiary carbon)?

Any ether containing a tert-butyl-oxygen bond can ionise after protonation to give the stable tertiary cation, which is trapped by iodide. For the phenyl ether the other fragment is phenol because the aryl carbon cannot be attacked. Ethyl methyl ether has no tertiary carbon and gives $\mathrm{CH}{}_3\mathrm{I}$ by SN2 instead.