There is a risky Asset $M$ and a riskless Asset $L.$ The efficient set of portfolios combining Asset $M$ and Asset $L$ is described as follows:

a$.$ It represents some lending at the riskless rate and the balance invested in Asset M$.$

b$.$ It represents some borrowing at the riskless rate with the initial wealth and the borrowed funds invested in Asset $M.$

c$.$ It contains Asset M$.$

d$.$ All of the above.