The correct answer is (a) A B+ -tree grows downwards
To explain: A B+ -tree always grows upwards. And In a B+tree – i)The path from the root to every leaf node is of the same length, so the tree is balanced. ii) Leaves are linked, so allow sequential searching. iii) An index is built with a single key per block of data rather than with one key per data record, so it is shallower than B-tree.