这位新选手成为了卫冕冠军的有力竞争者。

The new contestant emerged as a formidable ___challenger to the defending champion.

这位年轻的科学家作为传统理论的挑战者，提出了新的假设。

The young scientist, as a ___challenger of conventional theories, proposed a new hypothesis.

这家新兴科技公司正努力成为智能手机市场的有力挑战者。

The new tech company is striving to become a strong ___challenger in the smartphone market.