Sigma B Is a Stress-Induced Transcription Factor in Bacillus Subtilis $\beta$

Sigma B is a stress-induced transcription factor in Bacillus subtilis. Bacteria producing a sigma B-YFP fusion protein were exposed to constant energy stress and fluorescence pulses emitted by individual cells were detected by time-lapse microscopy. Could this result have been obtained using a sigma B- $\beta$ -gal fusion protein?

A) Yes. Hydrolysis of X-Gal by $\beta$ -galactosidase produces a blue product detectable by eye.
B) Yes. Hydrolysis of ONPG by $\beta$ -galactosidase in liquid medium produces an orange compound measurable by spectrophotometry.
C) Yes. It depends on how the construct is made with respect to the position of the RBS.
D) No. Whereas YFP fluorescence can be carefully observed and measured by time-lapse microscopy, $\beta$ -gal activity is measured as an average of the population as a whole.
E) None of the above.