B-tree of order n is a order-n multiway tree in which each non-root node contains __________

(a) at most (n – 1)/2 keys

(b) exact (n – 1)/2 keys

(c) at least 2n keys

(d) at least (n – 1)/2 keys

Enquiry is from B-Trees in portion B-Trees of Data Structures & Algorithms I

This question was addressed to me during an interview for a job.