Which of the following select statements could you use?

In Microsoft Dynamics AX 2012, you are creating a method on a table named VendTable. The method must return only the tax exemption number (VATNum). You need to return the VATNum for the vendor whose account number is 3000, by passing it in the _accountNum parameter. Which of the following select statements could you use? (Choose all that apply.)
A. (select VendTable where VendTable.AccountNum == _accountNum).VatNum;
B. (select firstOnly VATNum from VendTable having VendTable.AccountNum == _accountNum).VatNum;
C. (select firstOnly VATNum from VendTable where VendTable.AccountNum == _accountNum).VatNum;
D. (select firstOnly VATNum from VendTable where VendTable.AccountNum == _accountNum).AccountNum;