Please follow directions. This is a review paper. Make sure to be clear at first why you think it the answer

 Sentences 1, 3, 6, 8, 9, and 10 all have Restrictive Clauses.

The restrictive clauses distinguish or identify the subject and avoid vagueness or confusion about who performed the action in the sentence.

Explanation: Non-restrictive clauses provide additional but non-essential information about the subject.

2.) Mr. Hoffer, whose family lives in Germany,

4.) Mr. Johnson, whose son attends the University,  

5.) Thomas Jefferson, who was born on the frontier,

7.) My father, who was a country boy,

If the clause in #9 were non-restrictive, it would imply that all jet pilots are not in excellent physical condition, and not allowed to fly. That would be incorrect and cause a lot of problems.