In the following error spotting question, one part of the sentence may contain a grammatical mistake. Identify the part with the error or choose "No Error": "It had a bright blue / cover, which he was / careful not do soil. / No Error."

Introduction / Context:
This error spotting question focuses on a very common structure that appears after adjectives like "careful," "anxious," or "eager": the pattern "adjective + not to + verb." The given sentence describes someone taking care not to dirty a bright blue cover. Your job is to find the segment in which the standard grammatical pattern is broken and to understand how it should be corrected.

Given Data / Assumptions:

• The sentence is split into four parts:
  • (1) It had a bright blue
  • (2) cover, which he was
  • (3) careful not do soil.
  • (4) No Error
• The intended meaning is: "He was careful not to soil the bright blue cover."
• The phrase "not do soil" appears in part 3 and looks suspicious.
• The structure around "careful" needs to be checked.

Concept / Approach:
In English, after "careful," we normally use an infinitive with "to" when expressing what someone is trying not to do, for example, "careful not to slip," "careful not to disturb," or "careful not to drop the glass." The construction "careful not do" without "to" is incorrect. Therefore, part 3 contains the error and should read "careful not to soil" instead of "careful not do soil."

Step-by-Step Solution:
Step 1: Examine each part of the sentence for grammatical correctness. Step 2: Part 1, "It had a bright blue," correctly introduces the noun "cover" which follows. Step 3: Part 2, "cover, which he was," is a standard relative clause opening and is fine. Step 4: Part 3, "careful not do soil," sounds wrong. After "careful," the infinitive "to soil" should be used, preceded by "not to." Step 5: Conclude that part 3 contains the error; the correct phrase is "careful not to soil."

Verification / Alternative check:
Rewrite the full sentence with the correction: "It had a bright blue cover, which he was careful not to soil." This version is completely grammatical and natural. If we kept "not do soil," it would violate the usual pattern of "not to + verb" and sound wrong to a fluent speaker. Parts 1 and 2, by contrast, do not need any changes, and part 4 (No Error) cannot be correct because an error has been identified.

Why Other Options Are Wrong:

• 1: "It had a bright blue" correctly introduces the object "cover" that follows.
• 2: "cover, which he was" is grammatically fine as the beginning of a relative clause.
• 4 (No Error): Cannot be chosen, since part 3 clearly contains a structural error.

Common Pitfalls:
Students sometimes overlook small words like "to" after adjectives and focus instead on the larger parts of the sentence. Another common mistake is to think that inserting "do" before a verb will always help form a negative, but in this structure "not do soil" is not acceptable. Remember that after adjectives like "careful," "eager," "afraid," and "anxious," we normally use "to + verb" (for example, "afraid to speak," "eager to learn," "careful not to slip"). This will guide you to the correct correction in similar questions.

Final Answer:
The error is in part 3; the sentence should read: It had a bright blue cover, which he was careful not to soil.