When plant cells lengthen, it is called stretching elongation lengthening girth

The correct answer would be elongation.

Cell elongation is defined as the lengthening of a cell during differentiation of a cell. It takes place during growth of an organism or during movement in mature plants.

In plants, it is primarily regulated by light and plant hormones like auxin.

Auxin modifies the structure of the cell wall which helps the cell to elongate.

the answer is true when observing or determining population size, a direct observation is use, in which each organism is counted in a population or in an area. one benefit of this measure is that you get the exact population count but it will take a long time to  determine  the  size  of a  population.