The correct assertive sentence is “It is a matter of regret that he missed the connecting flight to New York.”
If there is ‘Alas’ in the exclamatory sentence, it is replaced by ‘It is a matter of regret that/ It is a matter of remorse that’ in the assertive sentence.
The structure of the assertive sentence will be- It is a matter of regret that/ It is a matter of remorse that + remaining part of the exclamatory sentence + a full stop (.) at the end.
Let’s see an example-
Alas! He has lost his memory in the car accident. (Exclamatory sentence)
It is a matter of regret that he has lost his memory in the car accident.(Assertive Sentence)
He must have lost his memory in the car accident. (Assertive Sentence)
Therefore, the Assertive sentence of the given exclamatory sentence will be- ‘It is a matter of regret that + he missed the connecting flight to New York.’
Option 1 is incorrect since it is an Interrogative sentence.
Option 2 is incorrect, 'must' is used to show compulsion.