Understanding Sentence Substitution

The question asks us to find the most appropriate substitution for the underlined phrase "shall not cause" in the sentence: "The bufotoxin present on a toad's skin can irritate you but touching a toad shall not cause you warts." This involves analyzing grammar, verb tense, and common idiomatic expressions.

Analyzing the Underlined Phrase

The phrase "shall not cause" is used to indicate a future negative certainty or prohibition. In this context, it's stating that an action (touching a toad) will definitely not result in warts.

Evaluating the Options

Let's examine each option to see why it might or might not be a suitable replacement:

• Option 1: was not cause This option uses the past tense "was not" but pairs it with the base form of the verb "cause". This is grammatically incorrect. The correct past tense form would require a past participle (e.g., "was not caused"). It also changes the tense from future/modal to past, which doesn't fit the sentence's meaning.
• Option 2: won't give This option uses "won't", which is the contraction of "will not". "Will not" functions similarly to "shall not" in expressing future negative certainty. Furthermore, the phrase "give warts" is a very common idiom associated with the myth about touching toads. While the original sentence used "cause", "give" fits the common saying better, making this a strong candidate for substitution, especially in the context of common expressions.
• Option 3: has not give This option uses the present perfect auxiliary "has not", which requires the past participle form of the main verb (e.g., "has not given"). "Give" is the base form, making this option grammatically incorrect.
• Option 4: do not cause This option uses the present tense auxiliary "do not". While grammatically correct in isolation ("Toads do not cause warts"), it changes the nuance from the future/modal sense of "shall not". The original sentence implies a specific instance or a general future rule, whereas "do not cause" is a simple present tense statement of fact. More importantly, it doesn't adopt the common idiomatic phrasing "give warts".

Selecting the Best Substitution

Comparing the options, Option 2, "won't give", is the most appropriate substitution. Here's why:

• Verb Tense and Modality: "Won't" (will not) effectively replaces "shall not" in conveying a future negative outcome.
• Idiomatic Accuracy: The common myth is stated as "touching a toad will give you warts". Therefore, substituting "won't give" aligns better with the popular expression, even though the original sentence used "cause" to state the factual inaccuracy. This type of substitution often aims to replace a phrase with a more common or recognized formulation.

Options 1 and 3 are grammatically incorrect. Option 4 is grammatically plausible but less contextually appropriate due to the shift in tense/modality and the failure to use the common idiomatic verb "give".