Explanation:

- Atal Bihari Vajpayee, the then Prime Minister of India, undertook a significant bus journey to Lahore. This effort was part of India's peace initiative towards Pakistan.

- The purpose of this journey was to engage in diplomatic talks and sign the Lahore Declaration. This agreement aimed to foster peace and cooperative relations between the two countries.

- Option 1: 1999 - This is the correct year when Atal Bihari Vajpayee traveled to Lahore for the peace initiative.

- Option 2: 1997 - This year does not correspond with the Lahore bus journey or the peace declaration.

- Option 3: 1991 - This was much before Vajpayee's tenure as Prime Minister.

- Option 4: 1994 - Similarly, this year does not align with the events in question.