Energy is a basic requirement for economic development because every sector of the national economy — agriculture, industry, transport, commercial and domestic — needs energy inputs to function.
Examples:
Without adequate energy, no development plan can remain operational.
Source: Conservation of Energy Resources, Chapter 5
The examiner expects you to state the direct link between energy and economic development, then back it with sector-wise examples (at least 2–3). The textbook explicitly lists the five sectors: agriculture, industry, transport, commercial, and domestic — mentioning these earns full marks. Keep examples crisp; do not elaborate into conservation or non-conventional sources unless asked.