Answer:
Line 4
Step-by-step explanation:
Line 4 states that our subject is 'slow and steady', implying that he has patience, and then describes the positive results of his scrupulous work: 'the issues have been solved and the car is running smoothly again'. The subject is able to reap the fruits of his labor, thus demonstrating that patience is a virtue.
The other sentences describe his engagement with his task in a more neutral way. In line 1, there is no mention of patience, only of his absorption in his task. In lines 2 and 3, the meticulous nature of his approach is described. Only in line 4 is the 'virtue' aspect of patience revealed.