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（心脏血管的)system 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 bums as many calories as running the same distance—if done in the correct manner and at a reasonable pace.
Start with a basic program that you can complete three or four times a week. This should include five main steps:
1) A beginning warm-up for about 5 minutes.
2) A little bit faster period of 5 minutes at medium level.
3) A 10-minute" burning" at a high level.
4) A 5-minute cool down period at a low level again.
5) A suitable walking pace of around 5 kilometers per hour will bum around 80 calories in 30 minutes.
According to the passage, walking is a simple way to ______.
A．lose weight
B．cure blood diseases
C．avoid heart attacks
D．strengthen heart functions