Here are the correct answers for each of the questions:

1. **C. amazing little old Chinese**
- The correct order for adjectives is: opinion, size, age, origin. "Amazing" (opinion), "little" (size), "old" (age), "Chinese" (origin).

2. **C. resistant**
- The correct form is "resistant" to describe bacteria that can withstand certain drugs.

3. **C. outwit**
- "Outwit" means to defeat or gain an advantage over someone by using intelligence or cunning, which fits the context of managing competition.

4. **A. doesn't it**
- This is the correct tag question; it mirrors the positive statement "Using social networks helps you share feelings and work with friends."

5. **D. was waiting**
- The past continuous "was waiting" indicates a background action occurring when he realized the street was too crowded.

6. **C. was invented**
- The correct passive form is "was invented," indicating that the telephone was created at that time.

7. **D. now that**
- "Now that" suggests a reason for walking to work, as it implies that his new apartment's proximity to the office is a newly established situation.

8. **C. When the company has finished designing the product**
- This option correctly indicates a future action that will occur after the company finishes the product design.

So, the answers are:
1. C
2. C
3. C
4. A
5. D
6. C
7. D
8. C