Which best describes a chain reaction associated with a nuclear reaction?

The correct answer for the question that is being presented above is this one: "A) self-sustaining." The term that best describes a chain reaction associated with a nuclear reaction is self-sustaining.
Here are the following choices:
A) self-sustaining
B) weak
C) non-explosive

It is false that all types of exercise are appropriate at any age. Older people generally cannot do the same exercises that teenagers can, simply because their bodies can no longer take such risks and move as flexibly as they used to when they were younger. Thus, there are exercises which are appropriate for older people, others which only teens should use, some for babies, some for middle-aged people, it all depends on the age.