Here are the correct answers for each question:

**Question 1.** The disease can be caused by a variety of viruses, bacteria, and other small organisms that **contaminate** food or water.
**Answer: A. contamination** (the correct form is "contaminate")

**Question 2.** This attack will **exacerbate** the already tense relations between the two communities.
**Answer: D. exacerbation** (the correct form is "exacerbate")

**Question 3.** You can **strain** your muscles from sudden twisting or **overusing**.
**Answer: C. overusing** (the usage is awkward)

**Question 4.** Ten-year-olds have started wearing lipstick and make-up in **imitation** of the older girls.
**Answer: B. imitator** (the correct form is "imitation")

**Question 5.** Her fingerprints **matched** the prints that were taken from the crime scene.
**Answer: A. suited** (the correct form is "matched")

**Question 6.** London is famous for its museums and art **galleries**.
**Answer: D. galleries**

**Question 7.** There has been bad **blood** between the two families for years.
**Answer: A. blood**

**Question 8.** To the best of my **knowledge**, the chemicals which were found are not dangerous.
**Answer: B. knowledge**

**Question 9.** After the ceasefire, the situation in the capital **got** better.
**Answer: C. got**

**Question 10.** He's been given a clean **bill** of health by the doctor.
**Answer: A. bill**

**Question 11.** We want to make it more difficult for criminals to use the City of London as a venue for laundering **dirty** money.
**Answer: B. dirty**

**Question 12.** Ramirez is looking forward to a **fresh** start with his new team.
**Answer: C. fresh**

Feel free to ask if you have more questions!