In the next 40 years, the percentage of people in the United States over the age of 65 is expected to double. 【B1】______ the needs of this part of the populations a 【B2】______ to the ingenuity (足智多谋) of America. To a 【B3】______ degree, a society is judged by 【B4】______ it cares for those who can no longer care 【B5】______ themselves. High technology 【B6】______ the most startling advances in helping the elderly. In 【B7】______ to the wellknown artificial heart implantation (移植) , there are efforts underway to 【B8】______ artificial lungs, livers, and bones. An electric ear is 【B9】______ sy-five percent effective. The implants will 【B10】______ better medical care by 【B11】______ minute doses of drugs into the body continuously. For the older people, even the st tasks can be difficult, 【B12】______ impossible to perform. American business have responded 【B13】______ their needs with a 【B14】______ of inexpensive but useful 【B15】______ Companies have designed extra-efficient can openers that 【B16】______ people whose hands have become 【B17】______ weak to open cans easily. There are devices that allow people to pull on a pair of socks 【B18】______ straining their backs. Combs with long handles and U-shaped back brushes are 【B19】______ for those who can not reach as 【B20】______ as they could when they were young.

A．how
B．why
C．who
D．whom