In the following passage, some words have been deleted. Read the passage carefully and select the most appropriate option to fill in each blank.

On 14th April 1912, the Titanic received warnings all the day about (1)______ icebergs. The first message was received at 9 a.m. Similar messages (2)______. Around 9 p.m., Captain Smith (3)______ with his second officer, before retiring for the night. They knew that on such a clear, moonless night it would be (4)______ difficult to spot icebergs. Why did they not change the course of the ship and take the ice-free southern route? It remains one of the (5)______ mysteries surrounding the Titanic.