Another name sometimes used for conversational speech is
a. formal speech
b. informal speech
c. slang

The correct answer is:

b. Informal speech.

Conversational speech is also known as Informal speech. Speakers regularly apply informal speech with friends and relatives, in daily conversations and in personal letters. Informal speech can cover informal text messages and different types of written communication.

faith or loyalty when pledged in a solemn agreement or undertaking.