Read the following paragraph and answer the question that follows.

[1] being a good reader is somewhat like driving a car; both reader and driver must learn to shift gears skillfully. [2] just as road conditions that require slow, careful driving call for first gear, a difficult text requires slow, thoughtful reading to be understood and remembered. [3] similarly, the driver can shift to second gear if he wants to go slightly faster. [4] second gear is useful to a reader of textual material which is not difficult but which must be remembered. on the open road a driver shifts to third. [5] third gear in reading is used for pleasure reading of magazines or novels. [6] both reader and driver sometimes use passing gear. [7] this gear is particularly useful to a reader who wants to skim a chapter as a review for a test or to preview an article to determine whether he wishes to read it. [8] just as driving in first gear at all times is inappropriate and inefficient, reading speeds must be shifted to suit conditions.
what is the topic sentence? 1 ,2, 3, 4, 5, 6, 7, 8 or none