In which place [A,B,C, or D] in the paragraph below (from the attached passage) could this sentence be added?
“Second, it is not yet clear whether vitamin D supplements can reduce risk of severe asthma attacks in all patients, or whether this effect is just seen in those who have low vitamin D levels to start with.”
[A] First, the findings relating to severe asthma attacks come from just three trials: most of the patients enrolled in these studies were adults with mild or moderate asthma. [B] Further vitamin D trials in children and in adults with severe asthma are needed to find out whether these  patient groups will also benefit. [C] Further analyses to investigate this question are on-going, and results should be available in the next few months.” [D]