In this sentence improvement question, choose the correct form of the verb to complete: "LPG quickly _____ popularity as it was easy to use and did not tarnish vessels."

Introduction / Context:
This question tests your knowledge of tense consistency in narrative English. The sentence describes a completed event in the past, explaining how liquefied petroleum gas became popular as a cooking fuel. The verb form used in the blank must match the past context already established by the phrase as it was easy to use and did not tarnish vessels. Correct tense choice is essential for coherent description in reports and essays.

Given Data / Assumptions:

• Main subject: LPG.
• Blank verb phrase: quickly _____ popularity.
• Context verbs: was easy to use and did not tarnish vessels, both in past tense.
• Four possible verb forms are given as options.

Concept / Approach:
Because the sentence is describing a completed change in popularity in the past, the correct tense is simple past, gained. Continuous forms like gaining would require a different structure, and future forms like will gain do not fit the clearly past context. We aim for a simple, straightforward statement of fact that aligns all verbs in the sentence in past time. Therefore, we need a past tense verb with no additional auxiliaries.

Step-by-Step Solution:
Step 1: Notice that the later verbs in the sentence are was and did not tarnish, both clearly in the past. Step 2: Decide that the earlier part should also reflect a completed past event. Step 3: Examine the options and identify gained as the simple past form of gain. Step 4: Check that LPG quickly gained popularity reads smoothly and logically. Step 5: Reject any option that breaks the tense consistency or grammatical structure.

Verification / Alternative check:
Read the full corrected sentence: LPG quickly gained popularity as it was easy to use and did not tarnish vessels. The sentence now offers a clear cause and effect description in past tense. If you try substituting will gain, you get a mismatch since the rest of the sentence still speaks in the past. Similarly, gaining popularity would need an auxiliary verb and a slightly different arrangement. This confirms that gained is the only suitable choice.

Why Other Options Are Wrong:
Gaining alone suggests either a continuous action or a reduced form in a different sentence pattern; it cannot directly follow quickly as a finite verb without a form of be.

Will gain is future tense, which conflicts with the already established past reference in was easy and did not tarnish.

No improvement would keep gain or another incorrect form in place, which does not match the given options or the correct grammar of the sentence.

Common Pitfalls:
Students sometimes focus on the adverb quickly and feel tempted to pick a progressive form, forgetting to match tense with the rest of the sentence. Another common error is not reading the entire sentence and therefore missing tense clues. Always read the complete context before choosing a verb form in sentence improvement questions.

Final Answer:
The correct verb form is gained, giving LPG quickly gained popularity.