Adults with more than a 12-month history of migraines were assigned randomly in a double-blinded study to receive treatment with experimental drug X (10 or 20 mg/day) or placebo. The primary efficacy measure was the reduction in severity of the migraine attacks. Enrollment was 1,200 subjects. Which of the following best describes the clinical phase of this study?

Phase III

Explanation:

The given condition fall in the trial phase (Phase III) of cinical study which aims to:

- Determine drug's effectiveness (primary goal)

- Determine long-term drug safety

- Confirm findings

In Phase III, randomised, double-blind, placebo-controlled, parallel group study is majorly to evaluate the efficacy and safety of placebo in episodic migraine prevention in children (6 to < 12 years of age) and adolescents (12 to < 18 years of age).  

The trial consists of four phases: screening; double-blind therapy period for 24 weeks in which placebo or Erenumab is given to subject as dose 1, dose 2 or dose 3 (based on the participant's body weight) once a month via subcutaneous injection; optional dose level blinded extension phase (40 weeks) which involves subjects recieve dose1, 2 and 3 of placebo, and at last it follows a safety follow-up phase for 12 weeks (after 16 weeks  of the last dose of investigational drug).

Hence, the clinical phase is phase III.

answer: - b cells

explanation: -

so, the b cells mediate their action by identifying the antigens present on the surface of the pathogens and then producing antibodies in return to mediate its effect.