The antecedent

Mock-up: 1. Every member of the sales team who (is, are) planning to take a vacation this summer must submit his or her request in writing by May 10. 2. All members of the sales team who (is, are) planning to take a vacation this summer must submit their requests in writing by May 10. 3. Which of the following three numbers (is, are) the correct answer for the mathematical problem shown above? 4. Which of the children who tried out this morning (has been, have been) selected for the three open positions on the team? Answers: 1. is (The antecedent of "who" is "member," which is singular.) 2. are (The antecedent of "who" is "members," which is plural.) 3. is (Only one number could be the correct answer to a particular mathematical problem, so the relative pronoun "which" is, in this sentence, singular.) 4. have been (Since three children were selected, the relative pronoun "which" is, in this sentence, plural.)