back 通常指对论点、行动、事业等的强有力支持。
uphold 既可指积极努力对陷入困境者的支持，也可指给某人在行动、道义或信仰上的支持。
support 含义广泛，多指在道义上或物质上支持某人，也可指对某项事业的支持。
sustain 侧重指连续不断的支持。
advocate 多指通过写文章或发表演说等来支持或拥护，往往暗示提倡某事或为某事辩护。
参考例句
1. How long will you sustain the rudeness of your boss? 对你上司的粗暴无礼你还能忍受多久?
2. But for how long can China sustain such growth? 但中国能够保持多久这样的经济增长？
3. All you have is enough water and dry biscuits to sustain one person for about ten days. 你所有的东西就是足量的水和能够让一个人维持十天左右的饼干。
英英解释
v.
1. lengthen or extend in duration or space
2. undergo (as of injuries and illnesses)
3. provide with nourishment
4. supply with necessities and support
5. be the physical support of; carry the weight of
6. admit as valid
7. establish or strengthen as with new evidence or facts
