This question tests your understanding of modal verbs and past tense usage in English grammar. Modal verbs express ability, permission, obligation, or possibility. The context describes a historical fact about Charles Dickens' childhood, indicating a lack of ability (could not go to school) due to an obligation (had to help his family).

Step-by-Step Analysis:

Step 1: Understand the context. The sentence describes a real situation from Charles Dickens' past. He was unable to attend school because he was obligated to work and support his family.

Step 2: Analyze the first blank. It requires a modal verb that shows a lack of ability in the past. The correct modal for this is couldn't (the contraction of 'could not').

Step 3: Analyze the second blank. It requires a phrase that shows a strong obligation or necessity in the past. The correct phrase for this is had to.

Step 4: Evaluate the options. Only one option correctly pairs "couldn't" (inability) with "had to" (obligation).

Final Answer: The most appropriate option is couldn't / had to.

The complete sentence is: Charles Dickens couldn't go to school at an early age, as he had to help his family.

Related Topic: Modal Verbs

Modal verbs are special verbs that behave irregularly in English. They are used to express ability, permission, obligation, prohibition, possibility, and probability. Common modal verbs include can, could, may, might, must, shall, should, will, and would. They are followed by the base form of another verb (e.g., could go, must help).

Related Topic: Expressing Past Obligation

To express a strong obligation or necessity that existed in the past, we use had to + base verb. This is the past tense form of 'must'. For example: "I had to finish my homework before I could play."

Key Formulae/Structures

1. Expressing Past Ability:
Subject + could/could not (couldn't) + base verb
Example: She could speak French when she was young.

2. Expressing Past Obligation:
Subject + had to + base verb
Example: They had to leave early to catch the train.