Consider the risk$-$return relationship in T$-$bills during each decade since $1950.$ Given this data, which of the following statements is correct?

$\backslash$table$[[$Decade$,$CoV$],[1950s,0\mathrm{.}40],[1960s,0\mathrm{.}33],[1970s,0\mathrm{.}29],[1980s,0\mathrm{.}29],[1990s,0\mathrm{.}24],[2000s,0\mathrm{.}55]]$

Since T$-$bills are backed by the full faith of the U$.$S$.$ government, computing the risk$-$return relationship for them is invalid.

None of these choices are correct.

The best risk$-$return relationship was during the $1950$s$.$

The best risk$-$return relationship was during the $1990$ s$.$