Answer:
4). To respect the elderly people.
Explanation:
The last sentence i.e. 'To respect the elderly people' is grammatically and lexically coherent. It correctly employs the infinitive(base form of the verb) and the followed preposition. The first option is incorrect as it employs the wrong preposition 'at' while the second and third options are incorrect due to inappropriate use of 'to.' Thus, option 4 is the correct answer.
