Question

it was to this______ he owed his life.a what

that

Answer 1

it was to this______ he owed his life.
a what b that

是选择填空吧。
应该是 a what,
it was to this_what_ he owed his life.
意思是：
这个（问题，事情）的关键在于（这里）他（到底）亏欠/给了他的妻子什么。
owe sb sth，给予某人某物，是owe的常见用法,
从句中，sth的部分没有找到，只能是用what来代替相应的部分，用that无法作为从句的句子成分（只是过度，连接），故这里要用what。