17) A

The passage describes a cause and effect situation. For this question you have to associate the cause described in the passage with the cause described in the options and the effect described in the passage with the effect described in the options.

Cause in passage = Whereabouts being kept secret or not
Cause in options = Tide being out or not out

Effect in passage = Risk management possible or not possible
Effect in options = Island can be reached or not

The passage states that if whereabouts were secret, risk management was possible. Replace this statement with ‘if tide is out, island can be reached’

The passage states that since whereabouts were not secret, risk management was not possible. Replace this statement with ‘since tide is not out, island cannot be reached’

So the answer should be:

‘If tide is out, island can be reached. Since tide is not out, island cannot be reached.’

This is given by option A only.

The other options confuse the cause and effect.