The question stem is referring to a conjugate vaccine. This is because conjugate vaccines convert T-independent antigens (polysaccharides) into T-dependent antigens by conjugating them with a protein. [FA2020 p127]

Remember that in order for a T-cell to be able to respond to an antigen via MHC, it MUST be a protein. Thus, T-dependent (dependent on T-cells) responses are to proteins. T-dependent responses are overall better because then B-cells can then undergo affinity maturation and class switching through interaction with T-cells. So, by conjugating bacterial polysaccharides to proteins, the immune response will be a more robust T-dependent reaction and will yield better protection. [FA2020 p103]

Conjugate vaccines exist for encapsulated bacteria (as the capsules are polysaccharide and would need to be conjugated to protein to improve response). These are Neisseria meningitidis, Haemophilus influenzae, and Streptococcus pneumoniae

You can remember these encapsulated organisms and their conjugate vaccine because they are THE SAME organisms that you become susceptible to when you have a splenectomy and which necessitate vaccination.

Just small addition to comment above:

Can also get to answer by way of elimination.

Oral Polio and Measles (part of MMR) are both live attenuated vaccines.

Diphtheria and Tetanus (both part of dTAP) are both toxoid vaccines.

You wouldn't be able to distinguish within these two categories, therefore the only answer left must be H. flu