Why do higher interest rates usually lead to currency values increasing?

a. Investors need to purchase the domestic currency to invest in that country and collect the higher interest rate.

b. The higher interest rate leads to inflation, which increases the price of currency together with all other products.

c. High interest rates encourage people to import more foreign goods, which will lead to more demand for the domestic currency.

d. Countries usually increase interest rates to fight recessions, and the resulting growth of the economy increases demand for that country's currency.