Question 21: Mark went on working despite he felt unwell. Correction: Change "despite" to "though". Corrected: Mark went on working though he felt unwell.

Question 22: Mary was upset last night because she had to do too many homeworks. Correction: Change "homeworks" to "homework". Corrected: Mary was upset last night because she had to do too much homework.

Question 23: I haven't visited my friends when I came to live in the city. Correction: Change "when" to "since". Corrected: I haven't visited my friends since I came to live in the city.

Question 24: He said he would go to England next week. Correction: No correction needed.

Question 25: You have to finished writing the report yourself. Correction: Change "finished" to "finish". Corrected: You have to finish writing the report yourself.