1. A bank holds different types of accounts for its customers: deposit accounts, loan accounts and mortgage accounts. Customers can be individuals or companies. All accounts have a customer, balance and interest rate (monthly based). Deposit accounts allow depositing and withdrawing of money. Loan and mortgage accounts allow only depositing. All accounts can calculate their interest for a given period (in months). In the general case, it is calculated as follows: number_of_months * interest_rate. Loan accounts have no interest rate during the first 3 months if held by individuals and during the first 2 months if held by a company. Deposit accounts have no interest rate if their balance is positive and less than 1000. Mortgage accounts have ½ the interest rate during the first 12 months for companies and no interest rate during the first 6 months for individuals. Your task is to write an object-oriented model of the bank system. You must identify the classes, interfaces, base classes and abstract actions and implement the interest calculation functionality.

2. Read about the Abstract Factory design pattern and implement it in C#.