8 Exercise increases heart .....

Analysis:

The sentence describes a benefit of exercise related to the heart. The word that completes the idiom 'heart rate' is 'rate'.

Breakdown:

• A muscle: Incorrect. While the heart is a muscle, the phrase is 'heart rate'.
• B flow: Incorrect. While exercise affects blood flow, the common phrase is 'heart rate'.
• C rate: Correct. 'Heart rate' refers to the number of times the heart beats per minute.

Translated Question:

8 Физические упражнения увеличивают частоту сердечных сокращений .....