Denm's _____really quiet,but now he is very outgoingA.used to be beB.used to being为什么选B?而不是A?

Denm's _____really quiet,but now he is very outgoing
A.used to be be
B.used to being
为什么选B?而不是A?

be used to do sth 被用于做某事
be used to doing 习惯做某事

a出现了另外一个谓语，但句子已经有谓语了。一个句子一个谓语