[填空题]
A hiker determines the length o7pl k) udmkp;a 9o2am(f a lake by listening for ed3 ytvk1 y2r m;vmy5+the echo of her shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s after shouting. Estimate thvmyr1vk;+de m3y25 ty e length of the lake. $\approx$ $ \times10^{ 2}$m
