Which of the following is a defining characteristic of living organisms?

1. Growth

2. Ability to make sound

3. Reproduction

4. Response to external stimuli

Response to external stimuli or to the environment in which an organism lives, is the most important characteristic of any living organism, besides growth and reproduction.

Growth and ability to make sound are some properties that can also be observed in non-living things. While virus (which is not included under living organisms) also show growth and reproduction.

Hence, these options are not true.