Transitional modifiers can appear at the beginning, middle, or at the end of the sentence. in which position would the modifier not require any commas? at the beginning at the middle at the end

Consider the title and souce of the following articles. which one is most likely to exhibit a bias? (a) how to roast beef," by the food editor of a magazine (b) americans experiencing greater fatigue than previous generations, " by a harvard researcher (c) "americans' worsening eyesight not related to computer screen usage," by the public relations director of a major computer manufacturer (d) "sharing the burden: a history of cooperation," by a college professor