In order to process a number typed in a TextBox the programmer must:

1. use the Val function to convert the Text value.

2. use the CDbl function to convert the Text value.

3. use the IsNumeric function to convert the Text value.

4. Both a and b.

5. All of the above.

Correct Option: D
Explanation:

To process a number typed in a TextBox, the programmer must convert the Text value to a numeric data type. This is necessary because the Text property of a TextBox control returns a string value, which cannot be used in mathematical operations without first being converted.

Now let's go through each option and explain why it is right or wrong:

A. use the Val function to convert the Text value: This option is partially correct. The Val function is one way to convert a string to a numeric data type, but it is not the only way. The Val function converts a string to a Double data type, so it may not be appropriate if the value in the TextBox is an Integer.

B. use the CDbl function to convert the Text value: This option is partially correct. The CDbl function is another way to convert a string to a numeric data type, but it is not the only way. The CDbl function converts a string to a Double data type, so it may not be appropriate if the value in the TextBox is an Integer.

C. use the IsNumeric function to convert the Text value: This option is incorrect. The IsNumeric function does not convert a string to a numeric data type. Instead, it checks whether a value is numeric and returns a Boolean value.

D. Both a and b: This option is correct. Using either the Val or CDbl function can convert a string to a numeric data type. However, the programmer should choose the appropriate function depending on the data type of the value in the TextBox.

E. All of the above: This option is incorrect. While options A and B are correct, option C is not a valid way to convert a string to a numeric data type.

Therefore, the answer is: D. Both a and b.