The correct answer is option 3 i.e. had known, could haveThe given sentence is a conditional sentence in the third conditional form. Let's look at the following points-The given sentence is a conditional sentence, conditional sentences show a possible cause and effect situation A conditional sentence has two clauses that depend on each other to make sense, Conditional clause (often referred to as if-clause) is a dependent clause and the main clause is the independent clauseThe tense of these clauses determines the type of conditional sentence Now look at the following point-To understand the types of Conditional sentence look at the following description -If clause Main ClauseIf + Present Indefinite Tense Simple Future tenseIf + Past Indefinite TenseSubject + would + v1If + Past Perfect Tense Subject + would/ could + have +v3 Explanation The given sentence is conditional consisting of 'if clause' with a blank and 'Main clause' with a blank preceded by subject and followed by the third form of Verb,As the subject and the third form of the verb are given in the 'Main clause' we can easily conclude that the Tense of the 'If clause' will be in 'Past Perfect'The third type of conditional sentence has the form'-If + past perfect Tense -------------Sub + would/ could + have + v3Hence, as per the rule the correct option to be filled in the blank is had known, could have??Correct sentence-If she had known how to calibrate the instrument, she could have done the experiment.