Myasthenia, or chronic muscle fatigue, can be an issue for the elderly that can prevent them from living on their own and contribute to the deterioration of their quality of life. A physical therapist who works predominantly with elderly patients believes that group exercise classes may be more appealing to elderly patients and therefore increase retention in the programs. To gauge the relative effectiveness of these group exercise classes, he performs a pilot study. A random sample of adult men with myasthenia were prescribed two sessions a week consisting of 45 minute group discussions on lifestyle changes followed by 55 minute weighted exercise sessions. As an indicator of overall health, each subjects' grip strength was measured at the start and end of the seven-week study, with higher grip strength indicating better health. The therapist hopes that subjects in the study show improvement in their grip strength across the seven-week program. Let _B represent the population mean grip strength before participating in prescribed social activities, _A represent the population mean grip strength after participating in prescribed social activities, and _D represent the population mean difference in grip strength (before - after). Which of the following would be the null and alternative hypotheses for this pilot study?H₀: _B = _A and H_a: _{B A}H₀: _D = 0 and H_a: _D < 0 H₀: _B = _A and H_a: _B > _AH₀: _D > 0 and H_a: _D = 0H₀: _D = _B - _A and H_a: _D < _B - _A