For maximum benefit, you should exercise 5-7 times a week for 60 minutes and your heart rate should be between of your max heart rate.

60 to 80%

Explanation:

For maximum benefit, the heart rates during exercise regimes should be between 60 to 80% of an individual's maximum heart rate.

The maximum heart rate varies from individuals to individuals and largely depends on age. It is calculated by subtracting one's age from 220. For example, a person that is 40 years old would have a maximum heart rate of;

  220 - 40 = 180 beats per minute.

Such a person's heart rates during exercises should be between 108 and 144 beats per minute for maximum benefits.

a.metals can become magnetic if they have many spinning electrons that create magnetic fields.d.only some metals are attracted by magnets; these metals are called ferromagnetic.

d.wrapping an insulated wire around a metal with ferromagnetic properties and applying an electric current.

pretty sure it's false