The correct option is C Well
An interjection is a word or two (usually followed by an exclamation
mark), that expresses a sudden emotion. It is not grammatically
connected to the rest of the sentence.
Many a times, interjections do not require an exclamation mark and are followed by the comma. Also, some interjections do not express any emotion.
Option D: 'Well' as an interjection does not express any emotion. It is used to introduce a statement, particularly one in reply to a previous sentence.
When placed here, it relates to the given sentence as it appears to be in response to something. Hence option D is correct.
Option A: 'Alas' refers to sorrow or regret. It represents sad, unhappy emotions.
Option B: 'Eh' expresses surprise or is used while questioning something.
Option C: 'Ouch' expresses a sudden pain, for example, if your friend pinches
your arm a little too hard, you immediately exclaim 'ouch!'.
These options are not appropriate for the given sentence. Hence A, B and C are incorrect.