题目

阅读理解 O'Brien and Samantha Kassirer from the Northwestern University Kellogg School of Management conducted two experiments to determine the levels of people's happiness when they gave away money or when they spent it on themselves. The first experiment involved 96 college students receiving $5 every day for five days. They had to spend the money on the same thing each day. Researchers randomly asked the participants to either spend the money on themselves or give it to someone else, like through a tip or an online donation to charity. The participants ended each day by reflecting on th如上中图所示的电路中，若只需要灯L1亮，则需要闭合开关 ；要使灯Ll、L2串联，则应只闭合开关_ ；要使灯L1、L2并联，则应只闭合开关 ．