Clay decides to open a sandwich shop in his neighborhood. he keeps the costs of his sandwiches low so more people can afford to buy them. but clay also knows he has bills to pay of his own- such as for his house, his car, and for clothes for his children- so he can't just give away the sandwiches he makes. this is showing what economic principle? a) profit motive b) supply and demand c) market advertising d) spending and credit