A word series is given: yes, rain, alive, subtle. Choose the option that correctly completes the series.

Introduction / Context:
Here you are given a sequence of words and asked to choose the next word in the pattern from the options provided. The words seem unrelated in meaning, so the sequence is most likely based on a structural feature such as word length or letter pattern. This type of question checks observational skill and the ability to detect hidden numerical or positional patterns inside ordinary looking words. Recognising such patterns quickly is a key part of verbal reasoning practice for competitive examinations.

Given Data / Assumptions:
Series given: yes, rain, alive, subtle, ?
Options: airport, smoke, inch, fabulous.
We assume that the same rule is applied consistently from the first term to the last and that exactly one option fits the pattern without ambiguity.

Concept / Approach:
When the meanings of the words in a series do not seem related, one of the most natural checks is the number of letters in each word. Many reasoning questions intentionally use unrelated words so that candidates cannot rely on common sense and are forced to look at structure instead. The strategy is therefore to count letters in each term, look for a clear progression, and then select the option that extends this progression correctly. Other possible patterns, such as alphabetical arrangement or vowel count, can be checked quickly if the length pattern is not clear, but here the length pattern is very prominent.

Step-by-Step Solution:
Step 1: Count the letters in each given word. yes has 3 letters. rain has 4 letters. alive has 5 letters. subtle has 6 letters. Step 2: Observe the numerical pattern. The sequence of word lengths is 3, 4, 5, 6, which is a simple increasing pattern with a difference of 1 at each step. Step 3: Predict the length of the next word. Continuing this pattern, the next word in the series should have 7 letters. Step 4: Check the length of each option. airport has 7 letters. smoke has 5 letters. inch has 4 letters. fabulous has 8 letters. Step 5: Identify the option with exactly 7 letters. Only airport has 7 letters, so it fits the pattern perfectly.

Verification / Alternative check:
We can double check by seeing whether any other simple pattern might be present. The first letters y, r, a, s do not show a clear alphabetical structure. The last letters s, n, e, e also do not follow a simple progression. There is also no obvious thematic relationship among the words. Therefore, the length pattern appears to be the intended logic. Since airport alone has length 7, it uniquely continues the 3, 4, 5, 6 pattern as 7. This confirms our choice beyond doubt.

Why Other Options Are Wrong:
smoke has only 5 letters, which ignores the requirement that the sequence continues upward beyond 6 letters and instead repeats a shorter length that has already occurred.
inch has 4 letters and similarly breaks the increasing pattern by going backward to an earlier length.
fabulous has 8 letters, which skips directly from 6 to 8 letters and does not maintain the consistent step of plus one letter at each term.
Thus none of these three options follow the simple and consistent length based rule of the sequence.

Common Pitfalls:
A common mistake is to search for a deep relationship in meaning or to overcomplicate the question. Candidates may try to connect yes, rain, alive, and subtle conceptually and completely miss the structural pattern of increasing word length. Another pitfall is miscounting letters under exam stress, especially for words like subtle where silent letters can distract. Taking a brief moment to count letters accurately and write down the sequence avoids such errors. Always remember that in many word series questions, the simplest numerical or structural pattern is often the correct one.

Final Answer:
The pattern is an increasing sequence in the number of letters: 3, 4, 5, 6, so the next word must contain 7 letters. Only airport has 7 letters, so it correctly completes the series.