Present participle; Past participle - flattening - flattened Present - flatten - flatten - flattens - flatten - flatten - flatten Past - flattened - flattened - flattened - flattened - flattened - flattened Future - will flatten - will flatten - will flatten - will flatten - will flatten - will flatten Present conditional - would flatten - would flatten - would flatten - would flatten - would flatten - would flatten Present Perfect - have flattened - have flattened - has flattened - have flattened - have flattened - have flattened Past Perfect - had flattened - had flattened - had flattened - had flattened - had flattened - had flattened Future Perfect - will have flattened - will have flattened - will have flattened - will have flattened - will have flattened - will have flattened Past conditional - would have flattened - would have flattened - would have flattened - would have flattened - would have flattened - would have flattened Imperative - - - flatten - - - - - - - -