In a certain code language, "book is tough" is written as "fu la mi", "tough can easy" is written as "fu muk po" and "easy not book" is written as "ti po la". What is the code for the word "tough" in that language?

Introduction / Context:
This question presents a coded language where each English word is consistently replaced by a short code. By comparing multiple coded sentences that share some common words, we can determine which code corresponds to which word. Here we are specifically asked to find the code for the word "tough". This is a standard type of mapping puzzle in verbal reasoning.

Given Data / Assumptions:

• "book is tough" is coded as "fu la mi".
• "tough can easy" is coded as "fu muk po".
• "easy not book" is coded as "ti po la".
• Each English word has exactly one corresponding code, and each code corresponds to a single English word.
• The order of words does not matter for the mapping, only which code words appear with which English words.

Concept / Approach:
The key method is to look for common English words in different sentences and match them with common code words. Shared English words must correspond to shared codes. Once we know some mappings, we can deduce the remaining ones by elimination. To find the code for "tough", we look for sentences where "tough" appears and see which code word is common to both of their coded forms.

Step-by-Step Solution:
Step 1: Note that the word "tough" appears in the first sentence "book is tough" and the second sentence "tough can easy". Step 2: The codes for the first sentence are "fu la mi". The codes for the second sentence are "fu muk po". Step 3: Find the common code word between these two code sets. The word "fu" appears in both, while "la", "mi", "muk" and "po" do not appear in both. Step 4: Therefore, the common English word "tough" corresponds to the common code "fu". Step 5: As an additional check, look at the third sentence "easy not book" coded as "ti po la". We already know that "book" appears in the first and third sentences. Step 6: The code words shared between "book is tough" (fu la mi) and "easy not book" (ti po la) are "la". Thus "book" must be "la", which is consistent with "tough" being "fu".

Verification / Alternative check:
We can verify that "easy" appears in the second and third sentences and that the shared code word there is "po". That would mean "easy" is "po". This uses the same intersecting technique and confirms that each mapping is consistent. None of these assignments conflict, which supports the conclusion that "tough" corresponds to "fu".

Why Other Options Are Wrong:
The code "mi" appears only in the first sentence and is not shared with any sentence that contains a second occurrence of the same English word. The code "po" appears in the second and third sentences which share the word "easy", not "tough". The code "la" corresponds to "book" as shown above. Therefore, only "fu" can be the code for "tough".

Common Pitfalls:
A common mistake is to try to match codes with English words based solely on position instead of looking at which words are common between sentences. Another error is to assume that two different English words can share the same code, which is not suggested here. Always match common words with common codes and check consistency across all given sentences.

Final Answer:
The word "tough" is written as fu in the given code language.