Statement:\nPower (electricity) consumption per family has doubled during the last five years.\n\nConclusions:\nI. There is a lot of development in society.\nII. Power tariffs have become cheaper.\n\nWhich conclusion(s) follow(s) from the statement?

Introduction / Context:
From a single trend—household electricity consumption has doubled over five years—we must judge whether two broad conclusions are logically necessary: that society has developed a lot, or that electricity has become cheaper.

Given Data / Assumptions:

• Only stated fact: per-family electricity consumption today is ≈2× that of five years ago.
• No information about electricity tariff levels, subsidies, appliance efficiency, household size, income, weather, or lifestyle changes.

Concept / Approach:
Logical necessity requires that a conclusion hold in every scenario consistent with the given statement. We therefore test whether each conclusion must be true across plausible explanations for higher usage.

Step-by-Step Solution:

Verification / Alternative check:
Construct scenarios: (a) Tariffs increased, but appliance additions led to higher usage; (b) Tariffs decreased, leading to more usage; (c) No tariff change, but climate/remote work increased consumption. The statement holds in all three—therefore neither conclusion is necessary.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing correlation (higher usage) with causation (development or cheaper rates); assuming a single cause when multiple factors can explain the observation.

Final Answer:
Neither Conclusion I nor II follows.