sprintlength - Pre exams question relased by scrum.org

Yes, the good answer, 'D' is cumulative.

No more than 4 weeks + short enough for other reasons.

Depending on the context, 4 weeks could be too long

You could read it differently.

Where is it saying the answer is cumulative?

answer A and C could implicitly mean that it will take longer than one month.

' a'  and 'c'  doesn't say that is can't be longer than one month. They don't say anything about time..  

Time isn't the only consideration. It is also important to consider business needs such as the two mentioned.

Note that Development Team capabilities may constrain the optimal Sprint length, although they should not be a driving concern.

Yes, the Scrum Guide states that a sprint cannot be longer than 4 weeks.   Why did they decide on 4 weeks or less, though?

Learning Scrum is much more than memorizing the answers to questions.   It also involves understanding why the answers are correct.   That is why  a)  and  c)  are relevant in the exam question you posed.

Let me put it another way.

A,B and C are separate  answers and don't have anything to do with each other.

D says: ' All answers are correct'  yes together cumulatively they are correct , but separately they are not correct. And that is wat D is saying: All answers are (separately) correct.

A should say: Short enough to keep the business risk acceptable to the Product Owner, but within one month

C should say: Short enough to be able to synchronize the development work with other businesses, but within one month

OR 

D should say: All answers are cumulatively correct

 

The question is

The length of a Sprint should be

so the answers are stated just fine.

It would be wrong if the question was: "we know the sprint length is optimal if:"

But that question would not have a correct complete answer, since there are many more factors to consider.