You are answering a USMLE-style medical question. Question: Mutations in the ATP2A1 gene results in loss of function of the calcium ATPase pump, which is in the sarcoplasmic reticulum membranes of skeletal muscle in humans. This mutation results in a rare disease characterized by muscle cramping and stiffening that is usually most severe after exercise or strenuous activity and is typically relieved after affected individuals rest for a few minutes. Which of the following is expected in individuals with an ATP2A1 gene mutation? Options: A) Muscle relaxation time: decreased, cytosolic calcium concentration: increased B) Muscle relaxation time: increased, cytosolic calcium concentration: increased C) Muscle relaxation time: increased, cytosolic calcium concentration: no change D) Muscle relaxation time: no change, cytosolic calcium concentration: decreased Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.