The correct answer is C. Reduction in current.
Carrier lifetime is the average time that a charge carrier (electron or hole) remains in the conduction or valence band, respectively, before recombining with an oppositely charged carrier. A reduction in carrier lifetime means that charge carriers are more likely to recombine, which reduces the number of charge carriers available to carry current. This in turn reduces the current flowing through the semiconductor.
Alpha and beta are parameters used to describe the characteristics of a transistor. Alpha is the ratio of the collector current to the base current, and beta is the ratio of the collector current to the emitter current. Both alpha and beta are typically greater than 1. A reduction in carrier lifetime will not affect alpha or beta.
Voltage is the electrical potential difference between two points. A reduction in carrier lifetime will not affect the voltage across a semiconductor device.