The correct order for replication of a Retro Virus is?

In order to replicate, a virus first has to enter the host cell by attaching itself, so options c and d can go straight out of the window....

Most, if not all, retroviruses already have a number of (their own) enzymes that are already present within the viral envelope: Reverse Transcriptase (RT), Integrase and a Protease.

Have a look at HIV :

Once the virus has entered the host, the viral RT will copy the viral RNA to DNA, which is then inserted into the host's DNA by the viral Integrase This DNA is then transcribed back into RNA again, that will then be processed by the host's machinery.

This RNA codes for new copies of RT , Integrase and Protease to be incorporated in the newly manufactured Viruses.

Therefore:

1:Virus attaches (and enters);
2: RT produces DNA (from viral RNA);
3: Host transcribes this DNA back into RNA;
4: from this RNA new copies of RT are produced.

In a nutshell:
Attach>DNA>RNA>RT.

This would describe option a....