In spring 2020, American households started preparing more meals at home due to the COVID-19 outbreak. This meant that a larger share of their expenditures was spent on food items for use at home. In May 2020, the average price of such items rose by 4.5 percent relative to the corresponding price in May 2019. For all other consumer items, the average price during the same period remained unchanged. When calculating the overall consumer price index (CPI) for May 2020, the Bureau of Labor Statistics used the expenditure shares of food-at-home and all other items that it had calculated based on a household expenditure survey carried out in 2019. The inflation rate derived from the CPI calculated in this way :

A.is an accurate measure of the true cost of living increase for households in May 2020.

B.underestimates the true cost of living increase for households in May 2020

C.overestimates of the true cost of living increase for households in May 2020.

D.may underestimate or overestimate the true cost of living increase for households in May 2020.