Meaning: 'Added' means to include something extra or additional, in this case, a precaution to improve the experiment.

Wrong options:

• attached: 'Attached' implies physically connecting something, which does not fit the context of introducing a precaution.
• conected: 'Conected' is a misspelling of 'connected' and suggests a physical link rather than the inclusion of a precaution.
• increased: 'Increased' suggests a rise in quantity or degree, which does not apply to the context of adding a precaution.

Correct answer: separated

Explanation: The word 'separated' is appropriate as it indicates that the children were kept apart from the observers, which is the intended meaning in the context of the sentence.

Meaning: 'Separated' means to keep things apart or divide them, which accurately describes the action taken to prevent interaction between the children and the observers.

Wrong options:

• paned: 'Paned' refers to a window pane and does not relate to the action of keeping children apart.
• split: 'Split' implies a division but is less formal and does not convey the intended meaning of keeping apart in this context.
• divided: 'Divided' suggests a more permanent or structural separation, which does not fit the context of the temporary arrangement described.

Correct answer: convincing

Explanation: The word 'convincing' fits well as it describes the results as being persuasive enough to warrant further investigation, aligning with the context of scientific inquiry.

Meaning: 'Convincing' means capable of causing someone to believe that something is true or valid, which reflects Dr. Sheldrake's belief in the results' significance.

Wrong options:

• satisfying: 'Satisfying' implies fulfillment or contentment, which does not accurately reflect the scientific context of the results being persuasive.
• concluding: 'Concluding' suggests bringing something to an end, which does not fit the context of the results prompting further experiments.
• persuading: 'Persuading' is a verb form and does not fit grammatically as an adjective to describe the results.

Correct answer: precisely

Explanation: The word 'precisely' is suitable as it indicates the need for exactness in determining how the staring effect occurs, fitting well with the scientific tone of the sentence.

Meaning: 'Precisely' means exactly or accurately, emphasizing the importance of detailed investigation in the experiments.

Wrong options:

• really: 'Really' is informal and does not convey the level of exactness required in a scientific context.
• carefully: 'Carefully' suggests caution but does not imply the exactness needed for the investigation.
• definitely: 'Definitely' indicates certainty but lacks the precision aspect that is crucial in scientific research.

Correct answer: come about

Explanation: The phrase 'come about' is appropriate as it refers to how something happens or occurs, fitting the context of exploring the mechanism behind the staring effect.

Meaning: 'Come about' means to happen or occur, which is relevant to the inquiry into the staring effect.

Wrong options:

• be looked at: 'Be looked at' suggests observation rather than the process of how something occurs, which does not fit the context.
• set out: 'Set out' implies a plan or intention rather than the occurrence of an event, making it unsuitable here.
• be held up: 'Be held up' suggests a delay or obstruction, which does not relate to the inquiry into how the staring effect happens.