lifeblood

1. N-SING The lifeblood of an organization, area, or person is the most important thing that they need in order to exist, develop, or be successful. 生命线[usu with poss]

Small businesses are the lifeblood of the economy. 小型企业是经济的生力军。

Coal and steel were the region's lifeblood. 煤炭和钢铁曾是这个地区的生命线。