Explanation:

Sand is a naturally occurring granular material composed of finely divided rock and mineral particles. It is commonly found in riverbeds, deserts, and coastal regions. However, not all types of sand are suitable for construction purposes. Good quality sand is essential for the construction industry as it is a key ingredient in concrete and other building materials.

The correct answer to the question is option 'C' - sea. The reasons why good quality sand cannot be obtained from the sea are as follows:

1. Salt Content: Sea sand contains high levels of salt, which can cause corrosion in steel and other metals used in construction. The salt content can also affect the setting and hardening of concrete, reducing its strength and durability.

2. Impurities: Sea sand may contain impurities such as shells, rocks, and other debris that can affect the quality of the sand. This can lead to poor bonding of the sand with other materials, resulting in weaker structures.

3. Grading: The grading of sea sand is not consistent, which can affect the strength and workability of concrete. The particles may be too fine or too coarse, leading to poor compaction and reduced strength.

4. Environmental Concerns: The extraction of sand from the sea can have a negative impact on the environment. It can disturb the marine ecosystem and cause coastal erosion. This can lead to the loss of habitats for marine life and affect the livelihoods of local communities.

Conclusion:

In conclusion, good quality sand is an essential component in the construction industry. While sand can be obtained from various sources such as rivers and deserts, sea sand is not suitable for construction purposes due to its high salt content, impurities, inconsistent grading, and environmental concerns. Therefore, it is important to use only good quality sand in construction to ensure the strength, durability, and safety of structures.