ANS:D - all the above.

The provided statements outline the guidelines for determining whether shear reinforcement is required in an RCC (Reinforced Concrete) beam based on the shear stress developed within the beam. Let's break down each statement:

1. If the shear stress in a RCC beam is equal to or less than 5 kg/cm², no shear reinforcement is provided: This indicates that when the shear stress in the beam does not exceed 5 kg/cm², the beam is considered to be adequately resistant to shear forces without the need for additional shear reinforcement.
2. If the shear stress is greater than 4 kg/cm² but less than 20 kg/cm², shear reinforcement is provided: This statement suggests that when the shear stress falls within the range of greater than 4 kg/cm² but less than 20 kg/cm², shear reinforcement is deemed necessary to enhance the beam's resistance to shear forces. Shear reinforcement, such as stirrups or inclined bars, is added to prevent shear failure.
3. If the shear stress is greater than 20 kg/cm², the size of the section is changed: When the shear stress exceeds 20 kg/cm², the shear forces acting on the beam are considered excessively high. In such cases, simply adding shear reinforcement may not be sufficient to address the shear capacity issues. Therefore, altering the size or dimensions of the beam section, such as increasing the depth or width of the beam, may be necessary to enhance its shear resistance.

Considering the above explanations, the correct statement among the options provided is: All the above.All the above. This option encompasses all possible scenarios regarding the provision of shear reinforcement in RCC beams based on the magnitude of shear stress developed within the beam.