Directions: Select the most appropriate filler(s) for the blank(s) such that the sentence makes coherent sense.

Investigators agree not only the systematic studies have failed to _________ answers to the questions of what causes schizophrenia, and also that the question itself has been ________ formulated.

'And' provides the continuity to the second part of the sentence. As the first part reflects the negative tone of the passage, subsequently the second part would also be negative. This implies that the investigators have been described saying that the studies have failed to answer some questions and the questions that have been formulated are incorrect in itself. Of all the options, 'yield' and 'incorrect' in option (4) fits our prediction and hence forms the answer.