COMAC C919
To be less dependent on western-built jet airlines the Chinese company COMAC designed its own Airbus A320 sized aircraft. Like many Chinese aircraft, it looks quite similar to the western counterpart. One key feature of the C919 are the two curved cockpit windows, of which the side windows have a V-shaped lower edge. Furthermore, the C919 has bent-up wing tips, which could be regarded as curved winglets. Other characteristics are very common: rectangular cabin windows, two small overwing emergency exits, large diameter turbofan engines, two wheel main and nose gears and a regular tail. (photo is modified original from WikiMedia, by AppleSteveGao)
Confusion possible with
Airbus A320 family
The Airbus A320 family looks very similar to the C919, in particular the A319neo and A320neo with their big engines. The A319 and A320 however have six cockpit windows and tall winglets, or small winglets up and down the wing tips.
Irkut MC-21
Like the Comac C919 the MC‑21 can be seen as a Russian version of the A320. To distinguish the MC‑21 from the C919 it is best to look at the cockpit windows, as the MC-21 has six of them. Additionally, the MC-21 has two large emergency exits before and after the wings, and for now the MC‑21 has no winglets. (photo: Dmitry Terekhov/WikiMedia)
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Airbus A220
Formerly known as the Bombardier CSeries, the Airbus A220 has the same basic configuration as the C919, and also four cockpit windows with a V-shaped lower edge of the side window. The A220 has a flat tail cone and canted winglets as main recognition points.
Boeing 737
To distinguish a Boeing 737 from the C919 look at the cockpit windows: these are the same as or similar to that of the Boeing 707 and 727. The older versions still have the two "eyebrow" windows above the normal cockpit windows. Also the nose is more pointed, the nose gear doors longer, and most 737s have a large, triangular dorsal fin.