Final answer:
A golfer with a metal club is vulnerable to lightning because the club can attract a strike. Seeking shelter under a tree is unsafe because trees can conduct lightning, posing a risk to anyone underneath.
Step-by-step explanation:
A golfer carrying a metal club on an open fairway is vulnerable to lightning because the metal club can act as a conductor that can attract a lightning strike. Lightning tends to strike taller objects and metal conducts electricity, making the golfer an easier target for a lightning strike.
As for seeking shelter under a tree, this is also unsafe. Trees can also attract lightning due to their height and can conduct the lightning strike to the ground. If lightning strikes a tree, the electrical current can travel along the tree and potentially injure anyone nearby. Wood is an insulator, but because lightning can carry such high voltage, it can travel through a tree to reach the Earth.