To ensure a good angle between the beam and the flow, you must either:

Which vessels are displayed at #1  and # 3?

What structure is located within the green box?

What does the Doppler waveform reveal about the vessel being imaged?

Which vessels aids in venous drainage from the superficial to deep venous system?

What structure is located at the blue arrow?

What is the imaging technique displayed within the vessel?

What vessel in the upper arm is identified at   #1?

What vessel is represented at the red arrow?

What information can be obtained from the color scale setting?