这位新选手是冠军头衔的有力挑战者之一。

The new player is one of the strongest ___challengers for the championship title.

这位年轻的科学家作为传统理论的挑战者，提出了全新的假说。

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

那个年轻人总是扮演挑战者的角色，激励朋友们尝试攀岩。

The young man often acts as the ___challenger, pushing his friends to try rock climbing.