This question tests the understanding of sentence structure, particularly indirect speech and word order in English grammar. Let's analyze the given sentence and options to determine the correct substitution.
The original sentence is: "Newton wanted to know why did the apple fall to the ground."
- The underlined part "know why did the apple fall" is incorrect because, in reported speech or indirect questions, the subject (the apple) comes before the verb (fell) without using auxiliary verbs like 'did'. The structure should be "know why the apple fell". Thus, the correct sequence is subject + verb.
- Let's evaluate each option:
- Option (a): "know that why did the apple fall" - This is incorrect because it incorrectly uses both 'that' and 'did', which do not follow the structure of indirect questions.
- Option (b): "know why the apple fell" - This is the correct option because it structures the indirect question properly, placing the verb after the subject with no auxiliary verb.
- Option (c): "know that why the apple fell" - This is incorrect; adding 'that' before 'why' is redundant and alters the sentence's meaning.
- Option (d): "No improvement" - Since option (b) provides a correct substitution, option (d) is not applicable.
- The correct answer is thus: "know why the apple fell". This option correctly constructs an indirect question, maintaining proper grammatical structure.
In conclusion, the substitution from option (b) improves the sentence by adhering to the grammatical rules for forming indirect questions.