Complete the sentence with the most suitable adjective: The life of a mosquito is _____, but very active.

Introduction / Context:
This sentence completion question tests a learner vocabulary and ability to interpret context clues. The sentence given is The life of a mosquito is _____, but very active. We need an adjective that logically contrasts with very active while describing the life span of a mosquito. Such questions are common in competitive exams to assess whether students can choose words that fit both grammatically and logically in real world contexts.

Given Data / Assumptions:

• Sentence: The life of a mosquito is _____, but very active.
• Options: long, passive, brief, important.
• The clause but very active suggests a contrast between the first adjective and the idea of activity.
• We assume general biological knowledge that mosquitoes do not live for a very long time.

Concept / Approach:
The phrase life of a mosquito refers to its lifespan, that is, how long it lives. In nature, mosquitoes have relatively short lives but often spend that time flying, feeding, and breeding actively. The contrast provided by but very active suggests that the first adjective should describe the length of life as short rather than long or passive. The word brief means short in duration, which fits perfectly. Therefore, The life of a mosquito is brief, but very active is the most logical and natural sentence among the options.

Step-by-Step Solution:
Step 1: Focus on the structure: The life of a mosquito is _____, but very active, where but introduces a contrast. Step 2: Recall that mosquitoes generally live for a short time rather than for many years. Step 3: Test the option brief, which means short in duration. The life of a mosquito is brief, but very active sounds natural and meaningful. Step 4: Test long: The life of a mosquito is long, but very active conflicts with known facts about mosquito lifespan. Step 5: Test passive: Passive describes behaviour, not length of life, and does not contrast properly with very active. Step 6: Test important: Important describes significance, not duration, and does not create the right contrast with very active either.

Verification / Alternative check:
We can verify by comparing with other common statements in science textbooks. It is common to read that the life of a mosquito is short or brief. For example, Some species live only for a few weeks. Describing the life as brief is therefore scientifically accurate. The clause but very active then emphasises that, despite the short duration, mosquitoes engage in a lot of activity in that period. Changing brief to long would contradict the biological reality. Replacing it with passive or important would shift the focus away from duration, making the sentence less coherent. This confirms that brief is the best choice.

Why Other Options Are Wrong:
long: This would mean that mosquitoes have a long lifespan, which is not true and also weakens the intended contrast with but very active.
passive: This adjective describes behaviour or attitude, but the life of a mosquito refers to its duration; moreover, passive does not fit with but very active.
important: Importance refers to significance, not length of life, and it does not contrast naturally with very active in this sentence.
brief: This correctly describes a short lifespan and forms a clear contrast with but very active.

Common Pitfalls:
Some learners may ignore background knowledge and choose an adjective simply because it sounds positive or fits grammatically. Others may focus too much on the word active and choose passive as an apparent opposite, forgetting that the blank should refer to duration rather than behaviour. To avoid such mistakes, students should always consider both the real world context and the logical relationship signalled by conjunctions such as but, and, or yet.

Final Answer:
The most suitable adjective is brief, giving the sentence The life of a mosquito is brief, but very active.