When does a natural monopoly arise?

a when a single seller buys or takes over all the competitors in the market
b when multiple sellers have access to scarce natural resources in a region
c when economies of scale occur over a relevant range of output
d when a limited number of sellers decide to jointly sell their products

Frugala is when sylvestor puts $2,000 into 10-year state bonds and $3,000 into 5-year aaa-rated bonds in steady hand hardware, inc. he buys the four state bonds at a 5 percent interest rate and the three steady hand bonds at a 6.5 percent rate. sylvestor also buys $1,500 worth of blue chip stocks, and $800 worth of stock in a promising new sportswear company that reinvests its earnings in new growth. 1. (a) what is the maturity for each of the bond groups sylvestor buys? (b) the coupon rate? (c) the par value?