INCIDENT. We also get the TOPIC of the passage. So, the first sentence- " A farmer was driving his wagon along a muddy country road after a heavy rain."Next is sentence D which states that horses could hardly drag the load which is in continuation with sentence B. "The horses could hardly drag the load through the deep mud."Next is sentence C as it states the result of sentence B. "At last it came to a standstill when one of the WHEELS sank to the hub in a rut."Last is sentence A. "The farmer climbed down from his seat and STOOD beside the wagon".So, the correct sequence is- "A farmer was driving his wagon along a muddy country road after a heavy rain. The horses could hardly drag the load through the deep mud. At last, it came to a standstill when one of the wheels sank to the hub in a rut. The farmer climbed down from his seat and stood beside the wagon."Hence, the correct answer is option 3.