1.imagine that somebody gives you a large sum of money to spend as you like （为什么要用as）
答：as表示“只要”的意思,它也可以表示原因,程度比because弱.
2.I’d just about given myself up for lost when I was spotted by a ship 为什么会是just about
答：just about的意思是“差不多,几乎”句意为,就在我几乎要放弃的时候,幸被一艘船发现获救.
3.The fact is that I earned my passage by working as an unpaid hand.which accounts for my appearance 为什么fact后面加is 和用as?
答：此句子为主系表结构,is为系动词,work as 是个固定短语,意为“从事...职业,做.工作.
3.He can do anything he wants with it 为什么要用with
with 表示伴随状态 （He can do anything he wants） with it