He was () a business suit.空里添wearing 还是介词in

表示穿衣可以用介词in,所以这里可以填介词in.
在阳光下,在灯下,在树阴下,穿衣、着装、冒雨等都要用in.
例：Don't read in dim light.切勿在暗淡的灯光下看书.
They are reviewing their lessons in the bright light.他们在明亮的灯光下复习功课.
They are sitting in the shade of a tree.他们坐在树阴下乘凉.
a prisoner in irons 带着镣铐的囚犯
He went in the rain to meet me at the station.他冒雨到车站去接我.
The poor dressed (clothed) in rags in old society.旧社会穷人们衣衫褴褛．
以及：in the bright sunlight 在明亮的阳光下
a merchant in disguise 乔装的商人
the woman in white (black,red,yellow) 穿着白(黑、红、黄)色衣服的妇女
in uniform 穿着制服
in mourning 穿着丧服
in brown shoes 穿着棕色鞋
in his shirt sleeves 穿着衬衫