What would have happened      , as far as the river bank? [ ]

A. Bob had walked farther

B. if Bob should walk farther

C. had Bob walked farther

D. if Bob walked farther

电阻应变计的电阻相对变化ΔR/R与应变ΔL/L=ε之间在很大范围内是线性的则k=（）。

A.ΔR/R/ε

B.ΔR/R/L

C.ΔR/R/ΔL

D.ΔL/L/R