在伊斯坦布尔时，我们参观了蓝色清真寺和托普卡帕宫。

While in Istanbul, we saw the Blue Mosque and the Topkapi ___Palace.

白金汉宫是伦敦最著名的地标之一。

Buckingham ___Palace is one of London's most famous landmarks.

国王的宫殿一直有重兵把守。

The king's ___palace is heavily guarded at all times.