(2014·沧州模拟)—I regret________you John has been fired.

—I can hardly believe my ears.He’s such a fine worker.

A．telling　

B．having told

C．to tell　

D．to have told

m阶B树的根结点若不是叶结点，那么它至多有______棵子树，至少有2棵子树。