Use String.Format(). Here is the example assuming transport and leave variables are already declared:
Dim myQueryTemplate As String = "SELECT employeeid, {0}, {1} FROM employees"
Dim myFinalQuery as String = String.Format(myQueryTemplate, transport, leave)
If you will debug that, the value of myFinalQuery will be:
"SELECT employeeid, transport, leave FROM employees"
Add more if needed. From my given example, the next parameter will be {2} and so on.