In this one word substitution question, choose the single English word that best replaces the description "full of twists and turns", a phrase often used for a winding road, path, river or a complicated plot.

Introduction / Context:
This English vocabulary question is from the topic of one word substitution. Instead of using a long description such as "full of twists and turns", you are asked to choose a single precise English word that carries the same meaning. Such questions are very common in competitive exams because they test how well you know exact, high level words that are frequently seen in reading comprehension passages, editorials and descriptive writing.

Given Data / Assumptions:

• The descriptive phrase is "full of twists and turns".
• You must select one word that can replace this entire phrase.
• Four alternatives are given, and exactly one is correct.
• The context can be a road, a path, a river or even a story line that bends and changes direction many times.

Concept / Approach:
The key to one word substitution questions is to understand the central idea of the phrase and then recall the single word that expresses that idea most accurately. "Full of twists and turns" suggests something that is winding, complicated or highly curved. In standard English, the adjective "tortuous" is used to describe roads, routes, arguments or procedures that are very twisty, indirect and difficult to follow. It is different from "torturous", which relates to torture or great physical suffering. Keeping this distinction in mind prevents confusion between similar looking words.

Step-by-Step Solution:
Step 1: Focus on the phrase "full of twists and turns" and imagine a road or path that curves again and again in different directions.Step 2: Recall English adjectives used for such roads or arguments, such as winding, twisting, zigzag or tortuous.Step 3: Look at the options and identify which one actually means "winding and highly curved".Step 4: Notice that "Tortuous" is the word that describes something with many hairpin bends, curves or indirect turns.Step 5: Confirm that the remaining options "Smooth", "Straightforward" and "Easy" do not carry any idea of twisting or turning and therefore cannot be correct.

Verification / Alternative check:
To verify, place the candidate word into a sample sentence. For example: "The hikers followed a tortuous mountain path to reach the village." If you mentally expand "tortuous", it becomes "full of twists and turns", and the sentence still makes perfect sense. If you replace it with "smooth path" or "easy path", the idea of many bends disappears. This simple substitution test confirms that "Tortuous" is the most accurate one word substitute for the given phrase.

Why Other Options Are Wrong:
"Smooth" refers to a surface that is even and without roughness, the opposite of difficult or twisty. "Straightforward" describes something that is simple, direct and easy to understand, which is again the opposite of twisting and complicated. "Easy" merely indicates low difficulty and has nothing to do with physical curves or changes in direction. None of these express the idea of many bends or turns, so they cannot substitute the given phrase correctly.

Common Pitfalls:
A frequent mistake is to confuse "tortuous" with "torturous" because they look and sound similar. "Torturous" relates to torture and severe pain, while "tortuous" relates to twisting, winding paths or complex arguments. Another pitfall is to choose a word that gives a general positive feeling, like "smooth" or "easy", without matching the specific meaning. Always focus on the exact image created by the phrase and then choose the word that recreates that image most accurately.

Final Answer:
The correct answer is Tortuous, because it is the standard English adjective used for something that is full of twists and turns and highly winding or indirect.