Use the Figure and the Following Description to Answer the Question

Multiple Choice

Use the figure and the following description to answer the question.
In a particular plant, leaf color is controlled by gene locus D. Plants with at least one allele D have dark green leaves, and plants with the homozygous recessive dd genotype have light green leaves. A true-breeding, dark-leaved plant is crossed with a light-leaved one, and the F1 offspring is allowed to self-pollinate. The predicted outcome of the F1 cross is diagrammed in the Punnett square shown in the figure, where 1, 2, 3, and 4 represent the genotypes corresponding to each box within the square.
Which of the boxes marked 1-4 correspond to plants with a heterozygous genotype?

A) 1 and 4 only
B) 2 and 3 only
C) 1, 2 and 3
D) 2, 3, and 4