The question mentions that it is about comparing sales between the years 1981 and 1979, with the unit of measurement being thousands.

Option 1: Rs. one hundred - We are considering sales in terms of thousands. Rs. one hundred is not substantial enough to be considered as it is too small a figure.

Option 2: Rs. ten thousand - This figure is still too small to exceed sales in the scale of thousands.

Option 3: Rs. one lakh - This is the correct answer. A lakh is higher than a thousand (one lakh equals one hundred thousand), suggesting a substantial increase in sales. Therefore, it implies that sales in 1981 significantly exceeded those in 1979.

Option 4: Rs. ten lakh - Though this is a larger figure than one lakh, without knowing the exact figures from the chart, we cannot determine whether the difference is this large. However, given that the correct answer is provided as option 3, we can deduce this is an overestimation.