Analysis. Answer options D and A are correct.
The CustomValidator control is used to provide a user-defined validation function for an input control. It determines whether or not the value of the input control passes customized validation logic. CustomValidator can be used to create client-side as well as server-side validation functions. The ControlToValidate property of the CustomValidator control specifies the input control to be validated. To validate the value entered in TextBox2, Patrick should use a CustomValidator control and write code to validate the date of birth.
The RequiredFieldValidator control is used to ensure that users do not skip an entry. Patrick should use two RequiredFieldValidator controls to ensure that both TextBox1 and TextBox2 have values.
Answer option C is incorrect. The CompareValidator control is used to compare a user's entry against a constant value, against a property value of another control, or against a database value using a comparison operator. It cannot be used to implement customized validation logic.
Answer option B is incorrect. The RegularExpressionValidator control is used to check that an entry matches a pattern defined by a regular expression. It cannot be used to implement customized validation logic.