Yuri created a formula for a button. The code is supposed to set the value of an existing field called title. He used the following formula: title:= @propercase (title); after the foumula runs ,the title field is null. Why? （）
- Athe value of one field cannot be set from the value in another field
- Bthe text string in the formula is set to null. Thus notes cannot validate the formula
- Cwhen setting the value of a field , the formula must be in the field‟s input validation event
- Dthe formula does not specify that title is an existing field. Thus it is interpreted as a temporary variable&e