You are looking at a cell through a microscope and see that a tetrad has formed, which phase of meiosis is the cell in?
metaphase i
anaphase i
telophase i
prophase i

The right option is; Prophase I

The cell is in the Prophase I of meiosis.  

Meiosis is a specialized type of cell division in which a diploid cell is divided to produce four haploid cells that are genetically distinct from the parent cell that produced them. Prophase I is the first phase of meiosis. During this phase, the chromosome duplicates and each homologous chromosome pair is visible as a tetrad (a group of four similar chromatids). Pairing occurs between the duplicated homologous chromosomes and there is physical exchange of chromosome parts (crossing-over) in this phase.  

the correct answer is:

a population changes in response to a change in the environment.