Modifying the verb tense of the clause the frogs were going to arrive a month ahead of schedule to future, the correct form of were going to arrive becomes 
In text 9A3CCC, a pronoun that introduces a relative clause is 
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Therefore is a suitable substitute for "So" (line 8).
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In "the inspectors" (line 5), the definite article can be omitted.
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The sentence "the inspectors recommend the introduction of homework charters (lines 5 and 6) can be expressed as follows: The inspectors recommend to introduce "homework charters".
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A person from "Poland" (line 12) is a Pole.
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The preposition up in crept up (line 6) is optional.
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The singular form of these (line 11) can be this or that.
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The ed in lasted (line 11) and introduced (line 15) is pronounced in the same way.
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In paragraph 3, using in spite of the fact that instead of Although will not affect the meaning of the sentence.