Answer is d) Lower pair

Sliding motion is an example of lower pair in which surface contact occurs.this pair is also known as prismatic pair....

The correct answer is option 'E' - higher pair.

Explanation:
In mechanical engineering, there are two types of pairs: lower pairs and higher pairs. When two moving elements have surface contact in motion, it is known as a higher pair.

1. Lower Pair:
- A lower pair is a type of pair in which the contact between the two elements is line or point contact.
- The relative motion between the two elements of a lower pair can be sliding, turning, or screwing.
- Examples of lower pairs include a cylindrical pair, prismatic pair, and revolute pair.

2. Higher Pair:
- A higher pair is a type of pair in which the contact between the two elements is surface contact.
- In a higher pair, the relative motion between the two elements can be rolling, twisting, or screwing.
- The contact between the two elements can be either a surface-to-surface contact or a surface-to-edge contact.
- Examples of higher pairs include a gear pair, cam and follower pair, and belt and pulley pair.

In the given question, it states that two moving elements have surface contact in motion. This indicates that the contact between the two elements is surface contact, which is a characteristic of a higher pair.

It is important to understand the distinction between lower pairs and higher pairs because they have different characteristics and applications in mechanical systems. Lower pairs are generally used for guiding and transmitting motion, while higher pairs are used for transmitting motion and force.

In conclusion, when two moving elements have surface contact in motion, it is referred to as a higher pair in mechanical engineering. This distinction is crucial in understanding the behavior and applications of different types of mechanical systems.