In the Avery, MacLeod, and McCarty experiment, the transforming extract from virulent bacteria was treated with DNase, RNase, or protease before being mixed with nonvirulent bacteria. The appropriate control for this experiment is to treat the transforming extract from heat-killed virulent bacteria with:

Nothing

Explanation:

A. Control variables generally entail little or no system change. To see if the method worked, the researchers required a positive control in which the heat-killed virulent bacteria invariably transformed the non-virulent microorganisms. This positive control involves adding "nothing" to both the heat-killed virulent bacteria before mixing them with the non-virulent bacteria.

answer: c. two haploid cells

explanation:

a tetrad is the foursome during meiosis made by two homologous chromosomes that have each already replicated into a pair of sister chromatids.