25. Ion channels are narrow pores that allow ions to pass through cell membranes. A particular channel has a circular across section 0.15 nm in radius; it opens for 1 ms and passes 1.0 × 104 singly ionized potassium ions. What is the current density in the channel? Note that one elementary charge is about 1.6 × 10−19 C.
(A) 5.0 × 106 A/m2
(B) 2.5 × 107 A/m2
(C) 5.0 × 107 A/m2
(D) 7.5 × 107 A/m2
(E) 1.0 × 108 A/m2

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統計： A(0), B(2), C(0), D(0), E(0) #3840135