Error Spotting – Choose the single segment (A–D) that contains a grammatical or usage error; select ‘‘All correct’’ only if the entire sentence is correct. Sentence: A) To solve a B) problem, one needs to have C) intelligent and firm D) determination

Introduction / Context:
This sentence probes adjective–noun compatibility and parallel noun formation. Some adjectives collocate naturally with people, not with abstract nouns like “determination.” Here, “intelligent” modifies a human agent, whereas “firm” can modify either a person or an abstract quality. The expected fix is to convert “intelligent” to the noun “intelligence.”

Given Data / Assumptions:

• Purpose clause: “To solve a problem …”.
• Head noun at the end: “determination”.
• Coordinated modifier segment: “intelligent and firm”.

Concept / Approach:
Maintain parallel grammatical form when coordinating qualities before a shared head noun. If the head is “determination,” pair it with another abstract noun to keep symmetry: “intelligence and firm determination,” or better, use two nouns (“intelligence and determination”) or two adjectives modifying a suitable head (“an intelligent and firm approach”).

Step-by-Step Solution:
1) Identify the head: “determination.”2) Ensure parallel form: adjective + noun should not be mixed awkwardly when the adjective does not naturally modify the head.3) Replace “intelligent” with the noun “intelligence” or change the head noun to “approach.”4) Minimal correction retaining the structure: “one needs to have intelligence and firm determination.”

Verification / Alternative check:
Paraphrase: “To solve a problem, one needs intelligence and determination.” This reads fluently and captures the intended meaning without collision in word classes.

Why Other Options Are Wrong:

• A–B: The infinitive opener and the main clause are standard.
• D: “determination” is a correct abstract noun; the mismatch originates in C.

Common Pitfalls:
Assuming any positive adjective can modify any abstract noun; ignoring parallelism in coordinated structures.

Final Answer:
intelligent and firm