Explanation:

- Let's break down the movement:

- The person first walks 100 meters in a straight line from the house.

- The direction of this first movement determines all subsequent directions.

- Afterward, he turns left and walks another 100 meters.

- Another left turn takes him 300 meters.

- A final right turn leads him 100 meters to the office.

- Given that his office is to the North-East of the house:

- The initial direction determines whether the final location aligns properly.

- Starting directly South from the house is the only way the described path would end in a North-East position, given the listed turn directions.

- Now let's examine the options:

- Option 1: North-West - This would not direct you North-East from the final position.

- Option 2: West - This direction also would not align correctly.

- Option 3: South - Starting South results in the final destination being North-East of the house.

- Option 4: South-West - This direction misaligns the final position completely.

- Therefore, the correct starting direction is Option 3: South.