Statement–Assumption — “Traffic jams on most city roads have become a regular feature during monsoon.” Assumptions: I. Materials used for road construction often fail under monsoon stress, creating potholes that slow traffic. II. The number of vehicles on the roads is much higher in monsoon than in other seasons.

Introduction / Context:
The phenomenon described is seasonal: jams become a “regular feature” during monsoon. We must identify the necessary underlying cause implicitly relied upon by the statement.

Given Data / Assumptions:

• Monsoon brings heavy rainfall causing surface damage, waterlogging, and reduced visibility.
• Road failure (potholes, rutting) slows traffic and increases congestion.
• Vehicle counts typically do not spike in monsoon; if anything, discretionary travel may reduce.

Concept / Approach:
A seasonal spike in congestion suggests a seasonal degradation in road conditions or traffic flow dynamics, not necessarily an increase in the number of vehicles. Therefore, the implicit assumption is about infrastructure performance under monsoon conditions (I), not a rise in fleet size (II).

Step-by-Step Solution:
1) I: If road integrity declines due to rain, jams becoming “regular” is explained. This is necessary and implicit.2) II: Claiming more vehicles in monsoon is neither typical nor necessary; congestion can worsen with the same or fewer vehicles if capacity drops. Hence II is not implicit.

Verification / Alternative check:
Basic traffic theory: When effective road capacity decreases (e.g., lanes narrowed by water/potholes), congestion rises even at unchanged demand.

Why Other Options Are Wrong:
II-only/Both/Either attribute cause to demand rather than the seasonal supply (capacity) shock indicated by monsoon effects.

Common Pitfalls:
Assuming “more vehicles” explains all congestion; capacity constraints can be decisive.

Final Answer:
if only assumption I is implicit.