Final answer:
The correct completion for the given sentence is option a) 'couldn't I?', as it is matching the negative question structure of the sentence.
Step-by-step explanation:
The correct option to complete the sentence 'I could clearly see that happiness, contentment, and peace depended more upon orderliness, thoughtfulness, and kindliness than upon genius, spasmodic effort, or keeping up appearances, couldn't I?' is a) couldn't I?. The sentence is structured as a negative question, which is appropriately matched with 'couldn't I?' to maintain the same form. The correct option to complete the sentence is 'could I?'