What are the twin characteristics of growth?

The correct answer/option is both a and b .

Explanation:
In biology, growth is defined as an irreversible, permanent increase in the size of an organ or its parts or even of an individual cell. It is a key characteristic feature of living organisms. The process of growth involves two primary twin characteristics:
1. Increase in mass: Living organisms grow in physical size and weight, which represents an increase in total biological mass.
2. Increase in number: Through cell division, multicellular organisms increase their cell count, and unicellular populations increase their individual counts. Thus, an increase in the number of individuals or cells is also considered a hallmark of growth.

Since both "increase in mass" (option a) and "increase in number" (option b) are the two key twin characteristics of growth, the correct choice is both a and b .