The adverb 'practically' here means almost complete. In the above sentence everything will be ready once the decoration is finished. Hence, option D is correct as it implies that the decoration is almost finished but not completed yet.
Effectively which is option A is the incorrect answer as its use in this sentence will imply that the decoration is actually finished whereas that is not the case.
The above sentence is expressing the fact that once the decoration is finished, everything will be ready soon.Option B, 'literally' would mean that we are emphasizing that the decoration is finished without it being literally true.Hence, it is incorrect.
The adverb 'relatively', option C, is used for comparisons. In the above sentence since no comparisons of any nature are being made, its use here would be incorrect.