Here are the corrections for the identified mistakes in the text:

1. **Question 11:**
- Original: "The kids are outside now. They play in the snow noisily."
- Correction: "The kids are outside now. They are playing in the snow noisily."
- Correct answer: **A** is incorrect, the correct form should be: "They are playing..."

2. **Question 12:**
- Original: "My father always gets up early because he isn't want to be late for work."
- Correction: "My father always gets up early because he doesn’t want to be late for work."
- Correct answer: **C** is incorrect, the correct forms should be: "doesn’t want..."

3. **Question 13:**
- Original: "What is the text mainly about?"
- Correction: No error; the question is good.
- Selected Answer would be **B**: "The start and development of the blues."

4. **Question 14:**
- Original: "According to paragraph 1, the blues is a type of slow, sad music created."
- Correction: "According to paragraph 1, the blues is a type of slow, sad music."
- Correct answer: **D** is incorrect, the phrase "created" should be excluded.

5. **Question 15:**
- Original: "The word 'elements' in paragraph 1 is closest in meaning to."
- Correction: No error found; the question stands good.
- Selected Answer would be **C**: "parts."

6. **Question 16:**
- Original: "The word 'it' in paragraph 2 refers to."
- Correction: No error; the question is fine.
- Selected Answer would be **C**: "the blues."

7. **Question 17:**
- Original: "Which of the following is NOT mentioned in the text?"
- Options should include a clarifying statement.
- Correction: Ensure that all answer choices are clearly differentiated.

After making these corrections, the document will be clearer and more grammatically correct.