1.I saw him looking at girls. [ At the gym]<br/><br/>2.I saw him ogling at girls. [ At the gym]<br/><br/>3.I saw him ogling girls. [ At the gym]<br/><br/>4.I saw him ogling. [ At the gym]<br/><br/>The verb ogle is both transitve and intransitive, according to the dictionaries.<br/><br/>So even my fourth sentence will pass the test.<br/><br/>I know my first sentence is fine.<br/><br/><span style="color:#ff0000;">Our native English speakers could tell me whether the second, third and fourth sentences are fine.</span><br/><br/><b><span style="color:#0000ff;">It may be the verb ogle borders informal English. I have no clue!</span></b>