The correct answer is 'Mbps', which stands for 'megabits per second'. It is used to measure network transmission speeds, and it is correct because '100 megabits per second' translates directly to '100 Mbps'. The 'M' stands for 'mega', indicating million, and 'bps' stands for 'bits per second'. 'MBps' would be incorrect because it means 'megabytes per second', where a byte is 8 bits and not commonly used in representing network speeds. 'Gbps' represents 'gigabits per second', which is one thousand times faster than 'Mbps'. 'Kbps' represents 'kilobits per second', which is one thousand times slower than 'Mbps'.