Sentence Correction: Tenses - Present Perfect

Linnaean taxonomy sharply distinguished the class Aves from the class Reptila, but since evolutionary science discovered that an order within it - Crocodylia - is phylogenetically closer to birds, this has been overturned.

Incorrect.

This answer choice is stylistically flawed. The pronoun it is ambiguous because it can refer either to the class Aves or to the class Reptila. The pronoun this is also ambiguous because it is not clear what it is referring to.

[[snippet]]

Incorrect.

While this answer choice corrects the pronoun ambiguity mistakes in the original question, by replacing the ambiguous pronoun it with the noun reptiles and adding the word distinction to clear what the pronoun this refers to, it is grammatically incorrect. The plural verb are does not agree with the singular subject Crocodylia.

Well done!

This answer choice corrects the pronoun ambiguity mistakes in the original question, by replacing the ambiguous pronoun it with the noun reptiles and by adding the word distinction to clarify what the pronoun this refers to.

[[snippet]]

Incorrect.

This answer choice is stylistically flawed. The pronoun it is ambiguous because it can refer to any of the singular nouns in the previous part of the sentence: taxonomy, class, science, or order.

[[snippet]]

Incorrect.

While this answer choice corrects the pronoun ambiguity mistakes in the original question, by replacing the ambiguous pronoun it with the noun reptiles and adding the word distinction to clarify what the pronoun this refers to, it is grammatically incorrect.

The corrected sentence incorrectly uses the Past Simple (overturned) with the time expression since. Since is indicative of the Present Perfect because it indicates an action that began in the past and is still relevant/in progress at present.

an order within it - Crocodylia - is phylogenetically closer to birds, this has been overturned

Crocodylia - an order within reptiles - are phylogenetically closer to birds, this distinction has been overturned

Crocodylia - an order of reptiles - is phylogenetically closer to birds, this distinction has been overturned

the reptile order of Crocodylia is phylogenetically closer to birds, it has overturned this distinction

the reptile order of Crocodylia is phylogenetically closer to birds, scientists overturned this distinction

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