The word missing to make the sentence logical is a preposition, which is contained in option d. The idea of the sentence implies collaborative work. When a task is performed by a pair of individuals, the right preposition is between; whereas when referring to a group of individuals, it is necessary to use among. The hint to be able to select the right answer is "several people".
Answer:
1. D
2. A
3. C
4. B
5. C
6. B
7. A
8. C
Explanation: