The correct answer is option a plant that has only two alleles for a trait.
In order to perform the Mendel's experiment, the conditions should be similar to the Mendel's actual experiment. The Mendel experiments shows the presence of two alleles controlling a single trait. So, in order to study the plant as the Mendel did, the person should choose a plant which have two alleles for a particular trait.
The plant must be able to self and cross pollinate in order to study the Mendelian characteristics accurately. IF a plant carry only recessive allele, then the effect of the dominant allele cannot be studied, so, the plant carrying only recessive allele should not be studied. Studying three allele coding for the same trait would be difficult to study the Mendelian characters, so, this plants should not be examined to study Mendel's experiment.
