The question asks:

In which species is the underlined carbon $sp^3$ hybridised?

However, the actual structures/options A, B, C, D are missing in the prompt. Since hybridisation of the underlined carbon depends completely on the specific bonding arrangement in each option, the answer cannot be derived from the information provided.

1. What is needed to determine $sp^3$ hybridisation?

A carbon atom is typically:

• $sp^3$ hybridised if it forms four sigma bonds (tetrahedral arrangement)
• $sp^2$ hybridised if it forms three sigma bonds and one pi bond
• $sp$ hybridised if it forms two sigma bonds and two pi bonds, or one triple bond

So we must inspect the exact structure of the underlined carbon in each option.

2. Why the question cannot be solved as given

The options are shown as:

• A:
• B:
• C:
• D:

but no molecular species are visible. Therefore, there is no way to evaluate which underlined carbon is $sp^3$ hybridised.

3. About the stored answer

The stored correct answer is given as B, but without the structures, I cannot independently verify it.

Hence, I cannot honestly confirm that option B is correct from the provided data alone.