asp.net – Validate the duplicate rows in datatable C#

I have one datatable e.g”
dt:

RowId  | FirstName  | LastName |  City
1      | Jhanvi     | Singhania| Mumbai
2      | Ashok      | Kumar    | Meerut
3      | Jhanvi     | SInghania| Mumbai

Now, I want to just get the duplicate rows in another datatable. tweak part: not all columns will be compared just FirstName and LastName. I don’t want to compare RowId and City