7. Which statement regarding glycogen and its metabolism is correct ? 　 1. Highly branched glycogen is less soluble than unbranched glycogen. 　 2. Having more ends effectively increases the rate of glycogen synthesis and breakdown. 　 3. To enter glycolysis, glucose-1-phosphate must undergo isomerization to glucose-6-phosphate by phosphoglucomutase. 　 4. To replenish glucose in the bloodstream, glucose-1-phosphate must be hydrolyzed to free glucose by glucose-1-phosphatase. (A) 1, 2, and 3 are correct. (B) 2, 3, and 4 are correct. (C) 1, 2, and 4 are correct. (D) All are correct. (E) None is correct.