a. Giải thích tại sao động mạch của người không có van nhưng tĩnh mạch lại có van, giải thích tại sao?

Awave has a wavelength of 15 mm and a frequency of 6 hertz. what is its speed?

Which of these is a provisioning service people get from the ocean

Ras is a g-protein that is activated when a growth factor attaches to egfr. its activation results in the replacement of a gdp molecule with a gtp molecule, thus allowing a signal transduction pathway to be activated. considering the signal pathway illustrated on this page, what is one potential outcome of a mutation in the ras gene that leads to ras protein hyperactivity. be specific.