DNA fragment patterns in plants and how/what mutations are seen?

Plants of a particular species can either have the dominant wild-type phenotype, tall, or the recessive phenotype called dwarf. Genetic analysis has identified the stature gene, and DNA analysis of tall plants yields a DNA fragment of 7.5 kb corresponding to a portion of the gene. The wild-type gene map is illustrated, along with an autoradiograph showing DNA restriction fragments from a normal parental plant (T; lane 1), a tall plant that carries a copy of the mutant allele (T; lane 2), the two DNA fragment patterns observed in tall progeny plants (T; lanes 3 and 4), and the DNA fragment pattern seen in dwarf plants (D; lane 5).

question - Propose two mutational events that could cause the small DNA fragment that represents the mutant allele.

A. The mutant allele is caused by the addition of 4.0 kb of DNA to the left end of the gene.
B. The mutant allele is caused by point mutation(s) in the gene (a nonsense mutation, for example) which also creates a new restriction site exactly 4.0 kb in from the right end of the map.
C. The mutant allele is caused by the deletion of 3.5 kb of DNA from the right end of the gene.
D. The mutant allele is caused by the duplication of the gene into the 4.0 kb fragment of DNA on the left end of the map.
E. The mutant allele is caused by the deletion of 3.5 kb of DNA from the middle of the gene.


link to picture.
http://session.masteringgenetics.com/problemAsset/1511970/8/Sand.ch10.p24.jpg