The second generation phenotypes resulting from the cross of true-breeding monohybrid pollination will display a ratio of
4: 1
1: 2: 1
3: 1
none of the above

The answer is 3:1.

A - the dominant allele
a - the recessive allele

The parental generation (P) is AA and aa:
P               AA      x      aa
F1           Aa    Aa    Aa    Aa

F1 is the first generation of offspring. After their cross, we get the second generation of offspring:
F1            Aa        x         Aa
F2       AA       Aa     Aa     aa

So we have 3 dominant phenotypes (AA, Aa, and Aa) and 1 recessive phenotype (aa). The ratio is 3:1