What is the method to customize columns in DataGrid ?

We can use the Template Column for customizing columns in DataGrid.
Example: 

<asp:TemplateField HeaderText="Birth Date">
  <ItemTemplate> 
    <asp:Label ID="BirthDateLabel" Runat="Server" 

       Text='<%# Eval("BirthDate", "{0:d}") %>' />
  </ItemTemplate>
  <EditItemTemplate>
    <asp:Calendar ID="EditBirthDateCalendar" Runat="Server" 
      VisibleDate='<%# Eval("BirthDate") %>' 

      SelectedDate='<%# Bind("BirthDate") %>' />
  </EditItemTemplate>
</asp:TemplateField>

How can we format data inside the DataGrid ?

We can use DataFormatString Property to format the data inside the DataGrid.
If the DataFormatString property is not set, the field's value is displayed without any special formatting.
Example:

<Columns>  
 <asp:BoundField HeaderText="Product ID" DataField="ProductID" />  
 <asp:BoundField HeaderText="UnitPrice" DataField="UnitPrice" 

   DataFormatString="{0:F0}" />  
</Columns>

What is the difference between Resume, CV and Biodata?

Resume is used by those person who have not an experience
in same word which person is fresher....
CV is used by those person who have an experience
in same word which person is doing work for year or months....
Bio-data is used for marriage purpose only
Note : So don't give your bio-data to company for job......

Define candidate key, alternate key, composite key.

Any attribute that is uniquely identify a row in a table is 
candidate key for the table. We select one of the candidate 
key as Primary key. All candidate keys which are not chosen 
as "primary key" are Alternate keys. The key which uniquely 
identify the rows of the table  and which is made up of 
more than one attribute is called Composite key.
Example: 

In a class we have to select Class Monitor. 
So A, B,C and D stand for that post. So A,B,C and D are 
candidate for monitor so these are candidate key. We select 
B as monitor so B is primary key and A,C and D can be 
monitor but not selected as a monitor so they are 
alternative choice. So A,C and D are alternate key.
When two students of class work together in a project than 
they are composite key for the class.

Difference between Access specifiers and access modifiers ?

Access specifiers  
The access specifier determines how accessible the field is 
to code in other classes.You can optionally declare a field 

with an access specifier keyword: public,private,or protected.

Access Modifiers 
You can optionally declare a field with a modifier keyword: 
volatile and static.