Digital Audio Tape (DAT or R-DAT) is a signal recording and playback medium introduced by Sony in 1987. In appearance it is similar to a compact audio cassette, using 1/8" magnetic tape enclosed in a protective shell, but is roughly half the size at 73 mm x 54 mm x 10.5 mm. As the name suggests the recording is digital rather than analog, DAT converting and recording at the same rate as a CD (44.1 kHz sampling rate and 16 bits quantization) without data compression. This means that the entire input signal is retained. If a digital source is copied then the DAT will produce an exact clone. The format was designed for audio use, but through an ISO standard it has been adopted for general data storage, storing from 4 to 40 GB on a 120 meter tape depending on the standard and compression (DDS-1 to DDS-4). It is, naturally, sequential-access media and is commonly used for backups. Due to the higher requirements for integrity in data backups a computer-grade DAT was introduced.

The correct answer is "These networks were originally designed to serve sporadic and only occasionally heavy traffic". Ethernet networks were originally designed to work with more sporadic traffic than Token Ring networks.

The correct answer is "56". This is actually a bit of a trick question, since the actual key length is 64 bits. However, every eighth bit is ignored because it is used for parity. This makes the "effective length of the key" that the question actually asks for 56 bits.
The other answers are not correct because:
168 - This is the number of effective bits in Triple DES (56 times 3).
128 - Many encryption algorithms use 128 bit key, but not DES. Note that you may see 128 bit encryption referred to as "military strength encryption" because many military systems use key of this length.
64 - This is the actual length of a DES encryption key, but not the "effective length" of the
DES key.
Reference:
Official ISC2 Guide page: 238
All in One Third Edition page: 622