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Sentence Correction: Parallelism - (n)either A (n)or B

Archaeologists investigating evidence at the Cradle of Humankind excavation site have proven that around 1.5 million years ago early humans began to control fire either to cook food or in defense against predators.

This answer choice is grammatically incorrect. Either is followed by the verb to cook while or is followed by a noun (defense). This creates a Parallelism error.

What helps us identify this question as a Parallelism question as well as identify this mistake is the following Stop Sign:

(n)either... (n)or...

Whenever you come across this Stop Sign, make sure the sentence follows both Parallelism rules: either must be complemented with or and neither with nor; and the same part of speech that follows (n)either must also follow (n)or.

This answer choice is grammatically incorrect and repeats the original Parallelism error. Either is followed by the verb to cook while or is followed by a noun (defense). This creates a Parallelism error.

What helps us identify this question as a Parallelism question as well as identify this mistake is the following Stop Sign:

(n)either... (n)or...

Whenever you come across this Stop Sign, make sure the sentence follows both Parallelism rules: either must be complemented with or and neither with nor; and the same part of speech that follows (n)either must also follow (n)or.

This answer choice is grammatically incorrect and illogical and repeats the original Parallelism error. Either must be followed by or.

What helps us identify this question as a Parallelism question as well as identify the mistake is the following Stop Sign:

(n)either... (n)or...

Although this answer choice corrects the original Parallelism error by using a verb after either and a verb after or, it creates Redundancy by using the passive form (has been proven). Since there is another grammatically correct answer choice that does not use the passive form, it is preferable to this one.

Fantastic!

Either must be complemented with or, and the same part of speech that follows either must also follow or.

Archaeologists investigating evidence at the Cradle of Humankind excavation site have proven that around 1.5 million years ago early humans began to control fire either to cook food or in defense

Archaeologists investigating the evidence at the Cradle of Humankind excavation site have proven that about 1.5 million years ago early humans began controlling fire either to cook food in defense

Archaeologists investigating evidence at the Cradle of Humankind excavation site have proven that around 1.5 million years ago early humans began to control fire either to cook food or as defense

It has been proven by archaeologists investigating evidence at the Cradle of Humankind excavation site that around 1.5 million years ago early humans began to control fire either to cook food or to defend themselves

Archaeologists investigating evidence at the Cradle of Humankind excavation site have proven that around 1.5 million years ago early humans began to control fire either to cook food or to defend themselves