In the following question, out of the four alternatives, select the option which best expresses the meaning of the English idiom or phrase "tie the knot".

Introduction / Context:
The expression "tie the knot" is a very common English idiom that appears in newspapers, conversations, and competitive exams. This question checks whether you can recognise the figurative meaning of the idiom, which is quite different from its literal words. Understanding such idioms is essential for scoring well in English sections of exams and for following real-life English usage in media and literature.

Given Data / Assumptions:

• The idiom given is "tie the knot".
• We must choose the option that best expresses its meaning in everyday English.
• The options suggest different types of actions: creating problems, making serious decisions, signing a deal, or getting married.
• The context is general English vocabulary, not a technical domain.

Concept / Approach:
Idioms are fixed expressions whose overall meaning cannot always be guessed from the individual words. Literally, "tie the knot" might make you think about fastening a rope, but the idiomatic meaning is associated with marriage. Many cultures use the symbolic idea of tying a knot or joining two things together to represent marriage. In English, "tie the knot" specifically means to get married. The approach is to recall this established idiomatic meaning rather than interpreting the words literally.

Step-by-Step Solution:
Step 1: Read the idiom "tie the knot" and recognise that it is a common phrase used in talk about relationships. Step 2: Think of sentences where you have seen it: "The couple finally decided to tie the knot next summer." Step 3: Replace the idiom with each option and see which one fits: "The couple finally decided to put themselves into a problem" clearly sounds wrong and negative. Step 4: Try "make fateful decision": although marriage can be a big decision, native speakers do not use "tie the knot" with this meaning in a general sense. Step 5: Try "sign the deal": this fits a business context, not the usual context of a wedding. Step 6: Try "get married": "The couple decided to get married next summer" matches exactly how "tie the knot" is used. Step 7: Conclude that the idiom "tie the knot" means "to get married".

Verification / Alternative check:
You can verify the meaning by checking any standard learner's dictionary. They define "tie the knot" as to get married, usually in an informal or conversational style. You will also notice it used in entertainment news headlines when celebrities marry: "Famous actor ties the knot in a private ceremony." This confirms that the exam expects "to get married" as the correct answer.

Why Other Options Are Wrong:

• To put yourself into a problem: This is negative and suggests trouble, which is not what the idiom itself means, even though marriages can have difficulties.
• To make fateful decision: Marriage may be a serious decision, but the idiom is not used for all serious decisions, only specifically for marriage.
• To sign the deal: Refers to business agreements or contracts, and does not capture the emotional and social meaning of a wedding.

Common Pitfalls:
A frequent mistake is to overthink idioms and connect them to any situation that feels serious or binding. Students might feel that "make fateful decision" also involves a kind of tying, but English idioms are not that flexible. "Tie the knot" has a fixed established meaning: to get married. Always rely on memory of authentic usage, not loose associations, especially in exam conditions.

Final Answer:
The idiom "tie the knot" means to get married.