Suppose a microbiologist has created three partial diploid strains of E. coli, each with different genotypes for the lac operon genes. The researcher wants to determine whether the synthesis of lacZ mRNA is constitutive or inducible in each strain and whether the strain is able to utilize lactose as a carbon source.

Strain 1: cap⁻ I⁺ P⁺ O⁺ Z⁺/ cap⁺ I⁺ P⁺ O⁺ Z⁺
Strain 2: cap⁺ I⁺ P⁺ O⁺ Z⁺/ cap⁺ I⁺ P⁻ O⁺ Z⁺
Strain 3: cap⁺ I⁺ P⁺ O⁺ Z⁻/ cap⁺ I⁺ P⁺ O⁺ Z⁺

Which of the above strain is inducible in the presence of lactose?