Concept:The idiom "clutch at straws" refers to a desperate person trying anything to escape a bad situation, even when the chance of success is very small.
Explanation:When someone is drowning, they may grab at floating straws, which cannot really save them.
This idiom is used when a person is so hopeless that they are willing to grasp any available chance, however weak or unlikely it may be.
In the sentence, a desperate man may "clutch at straws" to save himself.
This means he is not choosing a brave, clever, or secret plan; he is simply seizing any opportunity that comes his way.
Look at the options: acting bravely, trying clever means, or using a secret strategy do not match the meaning of grasping at random, weak chances.
Only "seize any opportunity" fits the idea of accepting any possible help or chance in desperation.
Answer:B. seize any opportunity