In 1970, a consumer magazine in London came up with a whim to test the value of a diamond's investment. It cost ꠴00 to buy two 1.5-carat diamonds at a jeweler. With two diamonds, most merchants refused to pay cash, and the highest offer they received was ꠵00. If you consider the inflation rate at the time, this offer is equivalent to ꠱67 in 1970. What is the main point of the above text? ['The value of diamonds is relatively stable.', 'High inflation in the UK between 1970 and 1978.', 'Diamonds do not preserve their value.', 'Inflation is the most important factor affecting diamond value preservation.']