a. False. Motion artefacts occur in the phase-encoding direction regardless of the actual direction of motion and are usually seen as either a smearing (induced by random motion) or ghosting (periodic motion). 

b. True. Aliasing is encountered in the phase-encoding direction when a part of the patient that lies beyond the chosen field of view appears on the opposite side of the image (known as a wrap-around artefact). A field of view smaller than the object in the frequency-encoding direction does not exhibit aliasing as the frequency-encoded signals are electronically filtered to remove the frequencies outside the receiver bandwidth. Note that in 3D scans, aliasing can also occur in the slice-select direction, as 3D slice encoding also relies on a phase shift. 

c. False. Magnetic susceptibility artefacts are worse on gradient-echo sequences, which do not provide compensation for local magnetic field inhomogeneities. 

d. False. Because the chemical shift (difference in resonance frequency) between fat and water is proportional to the static magnetic field strength, the resulting artefacts may be more pronounced at higher field strengths. 

e. True. Ringing appears as alternating dark and bright lines parallel to a high-contrast interface and is due to insufficient sampling of higher spatial frequencies. It can occur along the frequency- or phase-encoding direction, but is more commonly seen in the latter (due to the phase matrix being smaller in order to reduce scanning time).