even 通常指平面上的各点或一条直线的各点处在同一平面或直线上。
flat 指光滑平整的表面，但不一定是水平的。
level 强调没有高低之处，且在同一水平面，可引申指才能相等或与相邻某物平行。
smooth 侧重指表面十分平滑，无任何粗糙的感觉。引申作圆滑解。
参考例句
1. Smooth your behaviour with your girlfriend. 在和你的女朋友相处时，你得文雅一些。
2. Smooth this dress with an iron. 用熨斗把这件衣服烫平。
3. The waves lashed the smooth cliff. 波浪冲击着光滑的峭壁。
英英解释
n.
1. the act of smoothing
2. make smooth or smoother, as if by rubbing
3. make (a surface) shine
4. free from obstructions adj.
1. having a surface free from roughness or bumps or ridges or irregularities
2. smoothly agreeable and courteous with a degree of sophistication
3. of the margin of a leaf shape; not broken up into teeth
4. smooth and unconstrained in movement
5. (music) without breaks between notes; smooth and connected
6. of motion that runs or flows or proceeds without jolts or turbulence
7. lacking obstructions or difficulties
8. (of a body of water) free from disturbance by heavy waves
