Read the passage about early steam vehicles and answer the question: "What was the main problem with Trevithick's Puffing Devil road locomotive?"

Introduction / Context:
This reading comprehension question asks you to identify the specific weakness of Richard Trevithick's "Puffing Devil" road locomotive, as described in the passage. Such questions test your ability to distinguish between issues faced by different inventors and to link the right problem with the right machine.

Given Data / Assumptions:

- The passage states that Trevithick built and demonstrated his "Puffing Devil" road locomotive in 1801. - It then notes that many people consider this the first demonstration of a steam powered road vehicle. - Immediately afterwards, the passage explains that "It was unable to maintain sufficient steam pressure for long periods." - Other problems in the passage relate to water supply issues with Cugnot's inventions and passenger carrying capability for Verbiest's model, not to Trevithick.

Concept / Approach:
To answer correctly, you must match the phrase "Puffing Devil road locomotive" to the sentence that describes its limitation. The passage clearly states that the problem was maintaining enough steam pressure for long periods. This distinguishes Trevithick's challenge from other inventors who had different issues, such as water supply or small scale models.

Step-by-Step Solution:
Step 1: Identify the part of the passage discussing Trevithick: "In 1801, Richard Trevithick built and demonstrated his Puffing Devil road locomotive..." Step 2: Read the following sentence carefully: "It was unable to maintain sufficient steam pressure for long periods." Step 3: Recognise that "It" refers to the Puffing Devil road locomotive. Step 4: Match this explanation to option C: "Its inability to maintain sufficient steam pressure." Step 5: Check option A, which describes Verbiest's small model that could not carry a driver or passenger, not Trevithick's machine. Step 6: Check option B, "Problems with the water supply system", which the passage associates generally with Cugnot's inventions, not with the Puffing Devil. Option D mentions a combustion engine, which refers to Niepce's Pyreolophore, not a steam locomotive. Thus, option C is correct.

Verification / Alternative check:
Re read where the passage mentions "His inventions were however handicapped by problems of water supply and maintaining steam pressure." This sentence applies to Cugnot, not Trevithick. A separate sentence for Trevithick's Puffing Devil explicitly states the issue: "It was unable to maintain sufficient steam pressure for long periods." This separation of details between inventors helps verify that each problem belongs to a specific machine.

Why Other Options Are Wrong:
Option A ("Its incapability to carry a driver or a passenger") is taken from the description of Verbiest's 65 cm long model vehicle for the Chinese Emperor. Option B generalises water supply problems, which the passage attributes to Cugnot's tractors and vehicles, not specifically to the Puffing Devil. Option D ("Its combustion engine design") is wrong because the Puffing Devil is described as a steam powered road locomotive; the combustion engine is discussed later with respect to Niepce's Pyreolophore.

Common Pitfalls:
When passages describe several inventors and multiple technical issues, students often mix up which problem belongs to which inventor. A good strategy is to underline or mentally tag each inventor's name with a brief keyword (for example, "Verbiest model", "Cugnot tractors water/pressure", "Trevithick Puffing Devil steam pressure", "Niepce internal combustion"). This mental mapping helps you quickly return to the correct sentence when answering detail based questions.

Final Answer:
Its inability to maintain sufficient steam pressure was the main problem with Trevithick's Puffing Devil road locomotive.