The DropDownStyle property of a ComboBox control determines the style of the control. It can be set to one of three values: DropDown, DropDownList, or Simple.
DropDown: This is the default style. It displays a text box and a drop-down list. Users can type in the text box and the drop-down list will display the options that match what they have typed.
DropDownList: This style displays a drop-down list only. Users cannot type in the text box.
Simple: This style displays a text box only. Users can type in the text box, but there is no drop-down list.
Therefore, the correct answer is A, DropDown, because this style allows the user to type in the text box and provides a drop-down list of options.