单项选择题

Walking is the easiest and simplest form of exercise. By putting one foot in front of the other, you can start to walk your ways towards a healthier lifestyle. Walking is an easy way to challenge the cardiovascular system (心血管系统), while at the same time building muscles. But to achieve these goals, a little more than a gentle walk around the block is required.
Walking actually burns as many calories (卡洛里) as running the same distance —— if done in the correct manner and at a reasonable pace (步伐). Start with a basic program that you can complete three or four times a week. This should include five main steps:
——A beginning warm-up for about 5 minutes.
——A little bit faster period of 5 minutes at medium level (中等速度)
——A 10-minute “burning” at a high level.
——A 5-minute cool down period at a low level again.
——A suitable walking pace of around 5 kilometers per hour will burn around 80 calories in 30 minutes.

In the first 5 minutes of walking, you should walk （）

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