must have been / had to be

[sakura-saku]

Hello there. I need your help.
I'd be grateful if you could answer the question below.


(a) The fire spread very quickly. It must have been arson.

Which of the below is correct as an equivalent of (a)? I suppose (b) is.

(b) The fire spread very quickly. It had to be arson.
(c) The fire spread very quickly. It had to have been arson.
(d) The fire spread very quickly. It has to have been arson.

[2006]

Originally Posted by sakura-saku

Hello there. I need your help.
I'd be grateful if you could answer the question below.


(a) The fire spread very quickly. It must have been arson.

Which of the below is correct as an equivalent of (a)? I suppose (b) is.

(b) The fire spread very quickly. It had to be arson.
(c) The fire spread very quickly. It had to have been arson.
(d) The fire spread very quickly. It has to have been arson.

(b) is the only one I would use, but you can also say 'It has to be arson.'
(c) and (d) are unnecessarily complicated.

[sakura-saku]

Originally Posted by 2006

(b) is the only one I would use, but you can also say 'It has to be arson.'
(c) and (d) are unnecessarily complicated.

Thank you!