1) While we reduce the number of vehicles, the speed of traffic can be increased.
While we reduce the number of vehicles, we can increase the speed of traffic.
2) Before I selected the new course, my teacher warned me of the difficulty of the course and how long it lasted.
Before I selected the new course, my teacher warned me of the difficulty and length of the course. / Before I selected the new course, my teacher warned me how difficult the course was and how long it lasted.
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