In English idioms, what does the phrase "run out of steam" most accurately mean?

Introduction / Context:
The idiom run out of steam comes originally from the age of steam engines, where steam provided the power to move trains or machines. In modern English, this phrase is widely used to describe people, projects, or activities that lose energy or momentum over time. Competitive exams often test such idioms to see if candidates understand figurative language and can distinguish between similar sounding options.

Given Data / Assumptions:

• The idiom given is run out of steam.
• The context is general English conversation, not a technical description of engines.
• Four possible meanings are offered.
• We assume the expression is used about effort, enthusiasm, or progress.

Concept / Approach:
When a steam engine runs out of steam, it literally stops because there is no more power. Translating this idea into daily life, the idiom run out of steam means that a person or activity loses the driving force, enthusiasm, or energy to continue at the same pace. We therefore search for an option that mentions losing impetus or enthusiasm, rather than continuing or increasing effort.

Step-by-Step Solution:
Step 1: Remember the original image of a steam powered machine slowing down when fuel is exhausted. Step 2: Map this image onto human behaviour, where energy or motivation can decrease. Step 3: Read each option and note which one speaks about loss of energy or drive. Step 4: Reject options that suggest the opposite idea, such as continuing or building interest. Step 5: Choose the option that directly captures the sense of losing momentum.

Verification / Alternative check:
Consider a sentence such as The project started well, but the team ran out of steam after a few months. In this sentence, the speaker clearly means that the team lost enthusiasm and stopped working as actively as before. It does not mean they continued despite loss of energy, nor does it have anything to do with money. Thus the meaning line up perfectly with the idea of losing impetus or enthusiasm, which confirms our selection.

Why Other Options Are Wrong:
To keep going even after losing all energy describes persistence despite tiredness, which is the opposite of stopping or slowing down because of low energy.
Have no more funds to proceed any further focuses on money, not on energy, motivation, or physical strength, and so it changes the core meaning of the idiom.
Build interest as you go along suggests increasing enthusiasm, which again contradicts the idea of something slowing down or fading away.

Common Pitfalls:
A common error is to assume that run out of steam always relates to financial resources because people sometimes talk about running out of funds. Another mistake is to confuse this phrase with expressions about persistence, like keep going or push through. To remember correctly, visualise an engine that stops when there is no more steam and relate that to your own feeling of fatigue during long tasks.

Final Answer:
The idiom run out of steam means to lose impetus, energy, or enthusiasm.