It is believed that if a book is ________，it will surely ________ the reader.

A．interested; interest

B．interesting; be interested

C．interested; be interesting

D．interesting; interest

设某循环队列的容量为50，如果头指针front=45(指向队头元素的前一位置)，尾指针rear=10(指向队尾元素)，则该循环队列中共有______个元素。