Assembling Complete Genomic Sequences Based on the Overlap of Sequenced

Assembling complete genomic sequences based on the overlap of sequenced fragments can be difficult because the sequenced fragments:

A) may be relatively short (50-100 nucleotides) .
B) may have errors in them.
C) may come from either DNA strand.
D) may overlap but come from different locations in the genome.
E) may actually come from bacteria, viruses, or other contaminants.