**Core Concept**
The trivalent oral polio vaccine (tOPV) is a live, attenuated vaccine that protects against all three serotypes of poliovirus: type 1 (PV1), type 2 (PV2), and type 3 (PV3). The vaccine is designed to induce mucosal immunity in the gut, providing a barrier against poliovirus infection.

**Why the Correct Answer is Right**
The correct answer is related to the composition of the tOPV. The tOPV contains live, attenuated viruses of all three serotypes. Type 1 and type 2 polioviruses are attenuated versions of the Mahoney and MEF-1 strains, respectively. Type 3 poliovirus is an attenuated version of the Saukett strain. The inclusion of type 3 virus in the tOPV is crucial for providing immunity against this serotype, which is less prevalent but still a significant concern in polio-endemic regions.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not provided. Please provide the remaining options to complete the explanation.

Assuming the correct answer is among the remaining options, let's continue:

**Option B:** This option is not correct because the composition of the tOPV does not include type 3 virus; instead, it includes the other two serotypes.

**Option C:** This option is not correct because the composition of the tOPV includes type 3 virus, but this option might be referring to a different vaccine or a different composition.

**Option D:** This option is not correct because the composition of the tOPV includes type 3 virus, but this option might be referring to a different vaccine or a different composition.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that the tOPV contains live, attenuated viruses of all three serotypes, making it a crucial component of polio eradication efforts. The tOPV has been instrumental in reducing polio cases globally, but its use has been phased out in favor of the inactivated poliovirus vaccine (IPV) in many countries.

**Correct Answer:** C. Type 3 virus is part of the trivalent oral polio vaccine.