It's letter C :) I think..
Answer:
Doppler effect is a change in frequency and wavelength of a wave. It is caused by the change in distance between the thing creating the wave (causer) and whatever is measuring seeing or hearing the wave (watcher or observer). Another word for "causer" is "sender".
HOPE THIS HELPED!!!!!!!!!!!!!! XDDDD
can be replenished over months, years, or decades.
Cause mammals are the only species that are well developed before birth unlike marsupial and monotremes
All above I think I don't know