Here are the corrections for each of the questions:

**Question 26**:
The incorrect part is **(B)** "goes". The correct form should be "go".
So the correct sentence is: "Does he usually go swimming with Tim twice a week after school?"

**Question 27**:
The incorrect part is **(D)** "yesterday morning." The phrase should be either "this morning" or "yesterday morning" but not both together; since "will leave" suggests a future action, the correct word should be "tomorrow" if it's meant to be future.
So the correct sentence could be: "The bus will leave the station at 6 a.m. tomorrow."

**Question 28**:
The incorrect part is **(A)** "take often". The correct wording would be "often take".
So the correct sentence is: "I often take up my hobby when I come back home from the Arts Gallery."

**Summary**:
- For Question 26: (B)
- For Question 27: (D)
- For Question 28: (A)