Answer: D
The answer is D because the information following "message" is the message. A colon is appropriate (as used in D) when the information after the colon describes or represents the word or phrase that comes before the colon.
The weather forecast for the day, or rather what we can assume the
predicted forecast is due to the preparations the family are making,
will likely be a hot and sunny day, with a lot of humidity. We can
establish this due to the fact that sunscreen is being packed, combined
with the fact that Becca will need her inhaler.
All you do is read the sentence and add add between then
