Question

complete the sentence.
. , but they are also powerful weapons that can deliver a potentially fatal kick to predators such as lions.
an ostrichs legs are not only exceptionally long
not only are an ostrichs legs exceptionally long

Explanation:

This involves English grammar rules for "not only...but also..." inversion. When "not only" starts a clause, subject-verb inversion is required. The second option uses correct inversion, matching the structure needed to connect with the "but also" clause that follows.

Answer:

Not only are an ostrich's legs exceptionally long