Imagine you have two tasks: Task A: Build a database of employees of a large company, with a functionality to quickly search for employee record based on his/her phone number. Task B: Build a database of friends, with a functionality to find a friend by his/her birthday, and once the friend is found, having the ability to find who among friends has his/her birthday next. What data structure (Hash/BST/BTree/Heap) would you use for Task A/B? Justify your choice.