__________ the teacher explained the concept well, the students understood ...

★ Adverb & Compound Sentences

__________ the teacher explained the concept well, the students understood it, __________ they could apply it effectively.

A. Once, and

B. Since, and

C. When, but

D. If, or

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__________ exercising regularly, you can maintain good health, __________ you can also reduce the risk of certain diseases.

A. Until, or

B. Since, so

C. When, but

D. If, and