Which of the following is the sixth (last) sentence of the passage?

Directions : Six statements are given below, which are jumbled in any random order. Only the fourth statement (d), which has been emboldened, is in its correct place. These statements will form a coherent and meaningful paragraph, when arranged in the correct sequence. Arrange the sentences in the right order and answer the questions that follow. (a) The space station has already surpassed that checkpoint by being active for 21 years, with plans to continue operations till 2030, but the limitations on the life-cycle of the station are catching up. (b) This orbital thermal cycling, coupled with dynamic loading, affects the longevity of the primary structure of the space station. (c) It was originally built to operate for 15 years.                                                           (d) The ISS goes through 16 rotations of the earth per day, causing extreme temperature changes on the exterior. (e) The side facing the sun can get heated up to 121°C while the temperature on the opposite, darker side can fall to –157°C, causing intense expansion and contraction of the building material. (f) The National Aeronautics and Space Administration (NASA) has announced plans to retire and decommission the International Space Station (ISS) by 2031.