这只袋鼠是个天生的跳跃高手，能轻松越过栅栏。

The kangaroo is a natural ___leaper, easily clearing fences.

这位年轻科学家是物理学领域的飞跃者，短短几年就取得了重大突破。

The young scientist was a ___leader in physics, making major breakthroughs in just a few years.