In the following passage, some words have been left out. Select the correct answer for the given blank: “One cannot help ___________ into the speculative mood in view of the sharp contrasts between the birds of the East and those of the West.”

Introduction / Context:
This final cloze question in the passage focuses on a common English idiom: “cannot help doing something.” The narrator is saying that when observing strong differences between birds of different regions, one naturally moves into a speculative or thoughtful mood. Recognising the fixed grammatical pattern that follows “cannot help” is the key to selecting the correct option.

Given Data / Assumptions:
- Sentence: “One cannot help ___________ into the speculative mood in view of the sharp contrasts between the birds of the East and those of the West.” - Options: to fall, fallen, falling, fell. - We assume standard idiomatic English where “cannot help” is followed by a gerund. - The phrase “into the speculative mood” suggests a movement or transition into a way of thinking.

Concept / Approach:
The expression “cannot help” is almost always followed by a verb in the “-ing” form (gerund) when it means “cannot avoid” or “cannot stop oneself from doing.” For example, “I cannot help laughing,” “She cannot help smiling.” Here, the verb that describes the mental movement is “fall”: we say “fall into a mood” or “fall into silence.” Therefore, the correct grammatical and idiomatic completion is “falling into the speculative mood.”

Step-by-Step Solution:
1. Identify the structure: “cannot help” usually takes a gerund (verb + ing) as its object. 2. The main verb is “fall,” as suggested by the idea of entering a mood. 3. Evaluate options: - “to fall” uses the infinitive form, which is not standard after “cannot help” in this sense. - “fallen” is a past participle usually used with “have” or “be,” not directly after “cannot help.” - “falling” is the gerund form and fits the pattern “cannot help falling.” - “fell” is simple past and cannot follow “cannot help” in this structure. 4. Therefore, “falling” is the only option that both fits the idiom and makes semantic sense: “cannot help falling into the speculative mood.”

Verification / Alternative check:
Substitute each option in place of the blank and read aloud: “cannot help to fall,” “cannot help fallen,” and “cannot help fell” all sound ungrammatical and are not recognised idiomatic forms. “Cannot help falling into the speculative mood” sounds natural and matches many similar expressions such as “cannot help thinking” and “cannot help wondering.” This test confirms that “falling” is correct.

Why Other Options Are Wrong:
- to fall: Infinitive form, not used after “cannot help” in this meaning; would be considered incorrect in standard written English. - fallen: Past participle that requires an auxiliary verb, such as “has fallen,” and does not fit directly after “cannot help.” - fell: Simple past tense, which is incompatible with the auxiliary structure “cannot help.”

Common Pitfalls:
Students sometimes overgeneralise and believe that any verb can follow “cannot help” in base form or infinitive form. However, the idiomatic structure “cannot help doing something” is fixed and widely used. Remember also that “fall into a mood” is a standard expression describing a shift into a mental state. Combining both patterns correctly gives “cannot help falling into the speculative mood,” which is fluent and accurate English.

Final Answer:
The correct word for the blank is falling, producing the phrase “One cannot help falling into the speculative mood …”.