Here are the correct options for each question:

**Question 13:** "I bought you some flowers." - "They're beautiful, but you ______________."
- **A. needn't**

**Question 14:** It’s unlikely that two students would write identical compositions without ______________.
- **A. one who copies the other**

**Question 15:** Company policy states that, upon arrival, all employees are ______________ at the front desk.
- **B. signing in**

**Question 16:** Contact lenses ______________ of acrylic are more transparent and less fragile than lenses made of glass.
- **C. are made**

**Question 17:** The accountant broke the law, so it would be irresponsible of the firm ______________.
- **B. not to fire him**

**Question 18:** I hope everything’s OK. They ______________ several hours ago.
- **A. were to have called**

**Question 19:** In case he asks, tell him that I’ve already read his e-mail and ______________.
- **D. wrote to him back**

Feel free to ask if you need further assistance!