The correct option is A Standard
Option A: 'Standard' is a level of quality.
Option B: 'Style' is a particular manner or technique.
Option C: The self is a person's essential being, different from other persons' traits and characteristics.
Option D: 'Stand' is an attitude towards a particular issue.
From these words, 'standard' is the most suitable, as it completes the sentence in meaning: rising prices have made it difficult to live the same quality of life as before.
Hence option A is correct.
The other words do not complete the meaning of the sentence, hence B, C, D are incorrect.