Question

incidentally means :

in such a manner as could not be otherwise

with obstinate determination and perseverance

in addition; by way of addition; furthermore

by the way (used to introduce a new topic)

Explanation:

The word "incidentally" is an adverb. Looking at the options:

• "in such a manner as could not be otherwise" is not the meaning of "incidentally".
• "with obstinate determination and perseverance" is not related to the meaning of "incidentally".
• "in addition; by way of addition; furthermore" is not the most common meaning of "incidentally".
• "by the way (used to introduce a new topic)" is the correct meaning of "incidentally". It is used to introduce a new topic in a conversation.

Answer:

by the way (used to introduce a new topic)