他在最后一刻退出了交易，让我们处境艰难。

He ___backed ___out of the deal at the last minute, leaving us in a difficult position.

如果关键投资者退出，整个项目可能会失败。

If a key investor ___backs ___out, the whole project might fail.

在签了合同后，她有了顾虑，决定退出。

After signing the contract, she had second thoughts and decided to ___back ___out.