C-09-Q084mediumsingle_mcqToilet cleaners often contain the base—aNH4OH\mathrm{NH_4OH}NH4OHbNaOH\mathrm{NaOH}NaOHcMg(OH)2\mathrm{Mg(OH)_2}Mg(OH)2dCu(OH)2\mathrm{Cu(OH)_2}Cu(OH)2