题干

神经纤维可分为有髓鞘和无髓鞘两大类,现代生物学认为,髓鞘是由多层类脂物质﹣﹣髓质累积而成,具有很大的电阻,经实验测得髓质的电阻率为ρ=8×106Ω•m.某生物体中某段髓质神经纤维可看做长为20cm,半径为4cm的圆柱体,在其两端加上逐渐升高的电压,当电压U=100V时,该髓质神经纤维发生反应,则引起该髓质神经纤维产生感觉的最小电流为(   )

A:0.15μA

B:0.31μA

C:0.43μA

D:0.62μA

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答案(点此获取答案解析)

B

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    Spanish River Park

    Location: 3001 Ocean Blvd.,Boca Raton.

    Admission: $16 per vehicle on weekdays,$18 on weekends and major holidays.

    Special Comments: About 95 acres,more than a half-mile of beach with lifeguards.No pets.1,680-foot nature path and large playground area.

    Food/Dining: Picnic areas with barbecue grills(烤肉架).Phone: (561)393-7811

    Restores: Restrooms and showers available.

    Red Reef Park

    Location: 1400 N.Ocean Blvd.,Boo2 Raton.

    Admission: $16 per vehicle on weekdays,$18 on weekends and major holidays.

    Special Comments: Developed beach (67 acres) with lifeguards.No alcohol or pets permitted.It offers grills and a small playground area.

    Food/Dining: Picnic areas available.Phone: (561) 393-7812

    Restrooms: Restrooms and showers available.

    South Beach Park

    Location: 400 N.Ocean Blvd.,Boca Raton.

    Admission: $15 per vehicle on weekdays,$17 on weekends and major holidays.

    Special Comments: 1,670 feet of beach,25 acres,lifeguards,955 feet of developed beach south of Boca Inlet with lifeguards.

    Food/Dining: Picnic areas available.Phone: (561) 393-7813

    Restrooms: Restrooms and showers available.

    Coconut Cove Waterpark

    Location: 11200 Park Access Road,Boca Raton.

    Admission: Adult $7; Children(4~12)$5; 3 and under free.

    Special Comments: The waterpark offers Sea Monster(怪物)walk pool,Meandering River,a waterslide and a waterfall.No alcohol or pets permitted.

    Food/Dining: Concessions.Phone: (561) 274-1140

    Restrooms: Restrooms and showers available.