tan20°+tan40°+

3

tan20°•tan40°
=tan（20°+40°）[1-tan20°tan40°]+

3

tan20°•tan40°
=

3

[1-tan20°tan40°]+

3

tan20°•tan40°
=

3

-

3

tan20°•tan40°+

3

tan20°•tan40°
=

3

故选A