Assertion–Reason (Vehicular emissions as an environmental concern)\nAssertion (A): Vehicular emissions are a cause of concern for environmentalists.\nReason (R1): Emissions contain several gases and particulates that are harmful to human health.\nReason (R2): In cities, emission levels from vehicles can be very high.\nSelect which reason(s) truly explain A.

Introduction / Context:
Environmental concern around transport arises from toxicity and scale. This item asks whether toxicity (R1) and elevated urban levels (R2) together justify the assertion (A).

Given Data / Assumptions:

• A: Vehicular emissions are concerning.
• R1: Composition includes harmful gases/particulates.
• R2: Urban emission levels often become high (density of vehicles, congestion patterns).

Concept / Approach:
Risk = hazard × exposure. R1 states the hazard; R2 describes higher exposure contexts. Both combine to elevate risk and justify the concern in A.

Step-by-Step Solution:

Verification / Alternative check:
Health studies link traffic emissions to cardiopulmonary morbidity; urban peaks are consistently documented—aligning with R1 and R2.

Why Other Options Are Wrong:
A or B alone under-explain; D ignores both hazard and exposure.

Common Pitfalls:
Forgetting that concern rises with both danger and dose.

Final Answer:
If both (R1) and (R2) are reasons for the assertion (A).