Answer: Option D.
Explanation:
The "skeleton" of a logic statement is usually:
If "something true" then "this is also true"
Where the correct way to write this is:
"if hypothesis" then "conclusion".
Or
"Conclusion" only if "hypothesis"
There are other ways to write a logical statement, but this gives a general idea.
The hypothesis is the part of a logical statement that gives the premise on which the conclusion is based.
Now, in our statement we have:
If an angle measures 120°, then it's an obtuse angle.
Here the premise, the thing that needs to be true "first" in order to go to the conclusion, is "an angle measures 120°"
Then the correct option is D.