Can I say,<br/><br/>(a) The log is floating (in / at / on the river). <br/><br/>(b) Ice skating is her hobby. / She likes ice skating as / for her hobby. <br/><br/>(c) (i) The firemen put out the fire on / at houses. <br/><br/> (ii) The firemen put out the fire from the burning houses.<br/><br/>(d) He put the ladder against the ladder.<br/><br/>(e) The lightning struck in the sky.