For the development of India, a strong and efficient infrastructure is essential. This includes the construction of roads, bridges, ports, railways, and other critical infrastructure that can facilitate economic growth and improve the standard of living for the citizens.
Step 1: Infrastructure development plays a crucial role in supporting economic activities, facilitating trade, and improving connectivity.
Step 2: While defence, agriculture, and health are also important for the development of a nation, infrastructure serves as the backbone for all other sectors. A strong infrastructure framework facilitates overall economic and social development.
Final Answer:
\[
\boxed{(C) \, \text{Infrastructure}}
\]