Watson goes to see Sherlock after time apart Sherlock is happy to see his friend Watson
The verb that agrees with the subject in the sentence is option C. knows. So the complete sentence should be, "Mookie, who has to be one of the smartest dogs in the world, knows at least 30 tricks". We used the singular, present form of the verb because we are stating a fact and the subject, which is "Mookie" is a singular subject.
The complete subject is The workmen
the complete predicate is repaired the damaged bridge