Final answer:
The correct statement is that enhancers can increase or decrease the rate of transcription. They are DNA sequences that bind transcription factors, and their location can be variable relative to the genes they regulate.
Step-by-step explanation:
The true statement regarding the effects of enhancers and transcription factors (TFs) on gene expression is D) Enhancers can increase or decrease the rate of transcription. Enhancers are regulatory DNA sequences that can be located at various positions relative to the gene they regulate: upstream, within the coding region, downstream, or even thousands of nucleotides away. Enhancers serve as binding sites for transcription factors or activators. These proteins engage with enhancers to modulate gene expression by increasing or decreasing the rate of transcription. Unlike enhancers, transcription factors bind to the promoter as well as other regulatory regions to help initiate and regulate transcription. They can either increase the efficiency of transcription by facilitating the binding of RNA polymerase to the promoter or prevent transcription if they act as repressors.