The key to this question is the word "however," which signals a contrast between what people believed and what Hall actually found.
- The Belief: Spices help preserve food (implying they kill or stop the growth of microbes).
- The Reality (The Contrast): If the belief was that spices are cleaners/preservers, the "however" tells us Hall found the opposite-that the spices themselves were actually crawling with microorganisms.

Blank (i): B. teeming with
- Why? "Teeming with" means to be full of or swarming with. This directly contradicts the idea of preservation. If a spice is supposed to preserve food but is actually full of bacteria, it is failing its perceived purpose.
- A. devoid of: This means "completely without." If spices were devoid of bacteria, they would be helping preserve the food, which aligns with the belief and ignores the "however."
- C. improved by: Bacteria do not "improve" spices in a culinary or preservative sense; this doesn't fit the logic of the sentence.
- D. destroyed by: While bacteria can degrade organic matter, the sentence is focused on the presence of the microbes within the marketed product.
- E. active against: This is a synonym for "killing" or "inhibiting." If spices were active against bacteria, they would be good preservatives, which again fails to create the necessary contrast.

Final Completed Sentence
Many people at that time believed that spices help preserve food; however, Hall found that many marketed spices were teeming with bacteria, moulds and yeasts.