If we imagine ourselves in the scene in which the witness speaks with a firm and confident voice saying "that is the man I saw", the most probable thing is that it convinces us because she is very sure of herself, the witness does not doubt it for a moment, she/he is stating it.
The word <u>averred</u> can be replaced by <u>stated</u> since they have the same meaning. Other synonims can be claim, declare or affirm.
Answer:
A. The results of the experiment showed a quantifiable decrease in oxygen levels.
Explanation:
The chosen sentence possesses a formal register with technical vocabulary related to science, which can be understood by professional scientists. For instance, the words <em>quantifiable </em>and <em>decrease </em>have a more academic style. Besides, the writing is impersonal and written in the third person.
The rest of the options are incorrect because they have contractions and they are too informal. Thus, their vocabulary contain casual expressions which do not follow the conventions of an academic style.
Its the second one, a valley! Hope this helps :)