Which of the following pairs are both alkalis?

• a$\mathrm{NaOH}$ and $\mathrm{KOH}$
• b$\mathrm{Fe(OH)_2}$ and $\mathrm{Cu(OH)_2}$
• c$\mathrm{CaO}$ and $\mathrm{CuO}$
• d$\mathrm{NaCl}$ and $\mathrm{KCl}$