Meaning: 'Participants' means individuals who are involved in a study or experiment, contributing to the research findings.

Wrong options:

• experimenters: 'Experimenters' refers to those conducting the study, not those being tested, making it contextually incorrect.
• investigators: 'Investigators' implies those who are researching, which does not fit the context of individuals being tested in the study.
• performers: 'Performers' suggests individuals who are showcasing a skill or talent, which is unrelated to the context of a research study.

Correct answer: basis

Explanation: The word 'basis' is suitable here as it indicates a foundation or regular schedule on which the testing was conducted, aligning well with the context of the research. The other options do not convey the same meaning.

Meaning: 'Basis' refers to the underlying support or foundation for something, in this case, the regularity of the testing.

Wrong options:

• circumstance: 'Circumstance' refers to a condition or fact affecting a situation, which does not fit the context of a regular testing schedule.
• situation: 'Situation' implies a set of circumstances, but lacks the specificity of a structured testing framework.
• condition: 'Condition' suggests a state of being but does not imply the regularity required in this context.

Correct answer: because

Explanation: The word 'because' introduces a reason, making it the correct choice to explain why the link between walking speed and bodily functions exists. It fits grammatically and contextually within the sentence.

Meaning: 'Because' is used to indicate the reason for something, in this case, explaining the relationship between walking and bodily functions.

Wrong options:

• therefore: 'Therefore' indicates a conclusion rather than a reason, making it contextually inappropriate here.
• instead of: 'Instead of' suggests an alternative, which does not fit the context of providing a reason for the correlation.
• so: 'So' implies a consequence rather than a reason, which does not align with the intended meaning.

Correct answer: which

Explanation: The word 'which' is a relative pronoun that introduces a clause providing additional information about the slower walking speed, fitting grammatically and contextually into the sentence.

Meaning: 'Which' is used to introduce a clause that gives more information about something previously mentioned, in this case, the slower walking speed.

Wrong options:

• also: 'Also' is an adverb indicating addition, which does not fit grammatically in this context as it does not introduce a clause.
• this: 'This' is a demonstrative pronoun that does not appropriately connect the clause to the previous statement about walking speed.
• it: 'It' is a pronoun that does not provide the necessary connection to the clause, making it grammatically incorrect in this context.