当他谈论公司未来时，声音中带着一丝乐观。

There was a note of ___optimism in his voice as he spoke about the company's future.

我们从未独自出国，心中充满了乐观、好奇和荒谬的恐惧的混合情感。

We had never been abroad on our own and our hearts were full with a mixture of ___optimism, curiosity and absurd fears.

他富有感染力的乐观主义帮助团队克服了无数挫折。

His infectious ___optimism helped the team overcome numerous setbacks.