Which organism was used by Beadle and Tatum to propose the one gene-one enzyme hypothesis?

In the lac operon, the $z$ gene codes for:

Which enzyme is the expression product of the $y$ gene in the $lac$-operon?

Which statement is correct for homeotic genes?

Consider the following statements of gene regulation and select the correct statements $:$
$(A)$ Expression of genes is regulated by metabolic,physiological,or environmental conditions.
$(B)$ Galactose can act as an inducer for the lac operon.
$(C)$ The operator region is adjacent to the promoter elements in most operons.
$(D)$ In the lac operon,lactose is transported into the cell through the action of permease.
$(E)$ Regulation of the lac operon by a repressor is referred to as positive regulation.

Which of the following statements is correct regarding the repressor of the $lac$-operon?