Answer:
C: gerund
Step-by-step explanation:
The verbal phrase 'Watching the lionness care for her cubs' has a gerund (Watching) functioning as a noun. The verbal phrases can be used as other parts of the speech: nouns, adverbs or adjectives. In this case the gerund corresponds to a noun, which is also part of the subject of the sentence : "Watching the lioness care for her cubs".