Select the most appropriate word to fill in the blank and make a meaningful sentence.

He was physically strong and became a ________ climber of high rocky cliffs.

daring

The most appropriate word to fill in the blank is daring.

The word "daring" means "willing to take risks or do dangerous things." This is the most appropriate word because it accurately describes how the person was physically strong and was willing to climb high rocky cliffs, which is a dangerous activity.

The other options are not as appropriate.

• Timid means "shy or hesitant." This does not make sense in the context of the sentence, because the person was not shy or hesitant to climb high rocky cliffs.
• Fearful means "feeling afraid." This does not make sense in the context of the sentence, because the person was not afraid to climb high rocky cliffs.
• Unwilling means "not wanting to do something." This does not make sense in the context of the sentence, because the person was willing to climb high rocky cliffs.