The correct answer is option 'C' - Deep beams.

- Deflection is the bending or deformation of a beam under the action of an external load. In beams, deflection is primarily caused by bending moments and shear forces.

- Transverse shear force refers to the force acting parallel to the cross-sectional area of a beam. It is responsible for the internal shear stress distribution within the beam.

- In slender beams, the depth of the beam is relatively small compared to its span or length. In such beams, the deflection caused by transverse shear force is usually negligible. This is because the shear stress distribution is relatively uniform across the depth of the beam and does not cause significant bending or deformation.

- Circular cross-section beams have a symmetrical shape, which helps in distributing the shear forces evenly across the cross-section. As a result, the deflection caused by transverse shear force is relatively small and can be neglected.

- However, in the case of deep beams, the depth of the beam is large compared to its span or length. This results in a non-uniform shear stress distribution across the depth of the beam. The shear stress is maximum at the neutral axis and decreases towards the top and bottom surfaces of the beam.

- Due to this non-uniform shear stress distribution, the deflection caused by transverse shear force becomes significant in deep beams. The bending and deformation caused by the shear force cannot be neglected in the analysis of deep beams.

- I beams are a specific type of beam with an I-shaped cross-section. The deflection caused by transverse shear force in I beams can also be significant, depending on the depth of the beam and the magnitude of the shear force. However, it is not a generalized statement that applies to all I beams. Therefore, option 'D' - I beams, is not the correct answer.

In summary, the deflection caused by transverse shear force is not negligible in deep beams, where the depth of the beam is large compared to its span or length.