TRUE. Standing has the advantage of moving the centre of gravity much lower and allows the bike to move about without throwing the rider around. The bike is also more manoeuvrable
FALSE. The bike will move around when travelling over loose sand - fact. The amount of movement can be limited by travelling faster however as the bike becomes more stable at speed. The correct choice of off road tyres is also a factor that makes the bike more controllable.
ANTI-TETANUS. Off road bikers get more than their fair share of scraps and grazes and should therefore keep up to date with their anti-tetanus inoculations. (once every 5 to 7 years)