41岁男性，腰痛伴右下肢放射痛3个月，反复发作，与劳累有关，咳嗽或用力排便时可加重疼痛。查体右直腿抬高试验40°阳性，加强试验．阳性。X线片示：L_4～5椎间隙变窄。

最可能的诊断为( )。

A．急性腰扭伤

B．腰₃横突综合征

C．腰椎管狭窄症

D．腰椎间盘突出症

E．梨状肌综合征

Which of the following statements is least accurate with regard to the efficiency of monopolistic competition （）

A. Consumers benefit from brand name promotion and advertising.

B. Promotion and advertising enable consumers to make more informed decisions.

C. Monopolistic competition is at least as efficient as perfect competition.