Why is there a silent b in the word thumb.

There are quite a few English words that contain letters that are not suppose to be said including: debt and write. These left out letters can often tell us about the history and origin of the word and some places in the world has these which can tell us about who lived there at the time. This is called etymology.

Hope that this answer helped. ☺

a. both connotative and denotative.

b. the colonies must seek protection from other nations.