The answer is reverse faults.
This type of listening response is called back-channel signal. This allows the speaker to know that the listener is attentive or willing to engage a conversation between them. It is shown through short utterances, facial expressions, head nods and others.
A car A house A phone they all can be renewable
the answer could be (very basic) since options arent given
Answer:

Explanation:
Molar mass of helium = 
for helium is 1.67
The velocity of helium in sound at any temperature is given by 
R is a constant 8.314 