<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A group of investigators are studying the effects of transcranial direct current stimulation tDCS on cognitive performance in patients with Alzheimer disease. A cohort of 50 patients with mild Alzheimer disease were randomized 1:1 to either tDCS or sham tDCS over the temporoparietal cortex. Both procedures were conducted so that patients experienced the same sensations while receiving treatment. After 1 week of observation during which no treatments were delivered, the two groups were switched. Neuropsychiatric testing was subsequently conducted to assess differences in recognition memory between the two groups. Which of the following best describes the study design?? A: Pretest-posttest, B: Crossover, C: Meta-analysis, D: Parallel group, E: Factorialn,  <response>: This is a question about study design. It describes a randomized controlled trial comparing tDCS to sham tDCS in patients with Alzheimers disease. Patients were randomized to receive either real or sham stimulation first, followed by a washout period, and then crossed over to receive the other treatment. After both treatments, cognitive testing was performed. The key aspects here are:- Randomization to tDCS or sham tDCS- Crossover design where each patient receives both treatments- Washout period in between treatments- Cognitive testing after both treatmentsThis matches the description of a crossover trial design.B: Crossover 