答案：B

题目分析：be worth doing值得（被）做……，句意：老城堡很值得参观。

点评：本题需要把握worth和worthy两个词的用法。表示值得做……,worth用法为：be worth doing；而worthy用法为：be worthy to be done或be worthy of being doing。valuable“有价值的”和reliable“可靠的”与题意不符合。