Why do we not use resistor to control a.c.?

What is heart burn? Why do we take antacids to control it?

Why do we use iodized salt?

Why is the choke advantageous to resistors in controlling current in an a.c. circuit?

Why do we see moonlight ?

Where do we find fossils?

Where do we find fossils ?

Why do we need to know the centre of mass of an object? For which objeects, its position may differ from that of the centre of gravity?

Why do we differ from our parents?