How can an economy have elements of all three economic systems

Economies can have characteristics of traditional, command and market economies. This is because there isn't really such thing as a pure market economy and traditional elements are very common. Command and market economies can both have elements of traditional economies, and market economies must always have some level of command economic structure for governmental control of very basic aspects of itself such as military, healthcare, etc. The USA is an example of this.

the right answer is the constitution