Task: Question Generation
Input (English): It was not long until Apple released their first portable computer, the Macintosh Portable in 1989. Although due to considerable design issues, it was soon replaced in 1991 with the first of the PowerBook line: the PowerBook 100, a miniaturized portable; the 16 MHz 68030 PowerBook 140; and the 25 MHz 68030 PowerBook 170. They were the first portable computers with the keyboard behind a palm rest and a built-in pointing device (a trackball) in front of the keyboard. The 1993 PowerBook 165c was Apple's first portable computer to feature a color screen, displaying 256 colors with 640 x 400-pixel resolution. The second generation of PowerBooks, the 68040-equipped 500 series, introduced trackpads, integrated stereo speakers, and built-in Ethernet to the laptop form factor in 1994.
Output (English): Which generation of PowerBooks introduced trackpads?