锻炼能改善你的血液循环。

Exercise improves your ___circulation.

众所周知，吸烟对血液循环有害。

Smoking is known to be harmful to blood ___circulation.

四肢血液循环不良会导致手脚冰冷。

Poor ___circulation in the extremities can lead to a feeling of coldness in the hands and feet.