0 not able to send back an echo (= a sound that reflects off a surface): --
The anechoic chamber is used to test microphone performance.
The ultrasound showed an anechoic mass located behind a normal bladder.
Those are lightweight building blocks made of some porous, anechoic material.
We can complete it step by step however long the road is and it can't be completed however short the road is if you don't even mark your footprint.
Можем да го завършим стъпка по стъпка, колкото и дълъг да е пътят и не може да бъде завършен, колкото и кратък да е пътят, ако дори не маркирате отпечатъка си.