A plant containing variation in genetic composition is an example of  _________.

$\text{Correct answer: A}$ 

$\text{Option (A):}$ 

$?$ The plant containing variation in the genetic composition comes under the gene pool of the organism. 

$?$ A gene pool contains the collection of different genes in a population of a specific species. 

$?$ This includes the genetic diversity of the population containing all the variants of different genes.

$?$ So plant containing variation in genetic composition come under the gene pool. 

$\text{Option (B):}$  

$?$ A chromosome is the condensed genetic material formed during cell division so that genetic material can be properly distributed between the daughter cells. 

$\text{Option (C):}$ 

$?$ Genetic resources are the genes that are found in plants and animals which are useful to humans.

$?$ These are essential genes whose expression is important for humans.

Hence, the correct answer is option (A).