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A rock sinks straight down from the surface of a pond, starting from rest and accelerating at an average rate of $2\ \text{m/s}^{ 2 }$ for the first $3\text{ seconds}$ of its motion. At the $3\text{-second}$ mark, the rock reaches its terminal speed and continues at that same speed for the remaining $30\text{ meters}$ of motion.

Which one of the following is closest to the total time it takes for the rock to sink from the surface to the bottom of the lake?

A

$5.0\text{ seconds}$

B

$6.2\text{ seconds}$

C

$8.0\text{ seconds}$

D

$8.5\text{ seconds}$

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