The correct answer is the third diagram, the one in which Earth's axis is slightly inclined with respect to Earth's plane of orbit.
Indeed, the inclination of the Earth's axis has the effect to expose to the sunlight a hemisphere more than the other: i.e. during the month of January, the axis is inclined so that the South pole is closer to the Sun than the North Pole, resulting in summer in the Southern Hemisphere and winter in the Northern Hemisphere; while during the month of August the axis is inclined so that the North pole is closer to the Sun than the South Pole resulting in summer in the Northern Hemisphere and winter in the Southern Hemisphere.
