The correct answer is option 4: 1, 2, and 3.

Statement 1 is true because rainfall, temperature, and vegetation do vary with latitude. As one moves closer to the poles, the temperature tends to decrease, and the types of vegetation and amount of rainfall also change.

Statement 2 is true as well. The difference between the longest day and the shortest day increases with latitude. This is because the Earth`s tilt causes uneven distribution of sunlight, resulting in longer days in higher latitudes during summer and shorter days during winter.

Statement 3 is also true. Indira Point is indeed located approximately at 6°45` N latitude, making it a part of the Indian subcontinent.

Therefore, all three statements are true, which is why the correct answer is option 4.