"I cannot support him."
Translation:Je ne peux pas le soutenir.
"lui" is an indirect object, "le" is a direct object. In this sentence, "him" is the direct object so it needs to be "le".
I gave the same answer. Lui/le is explained above, but can anyone explain the difference between supporter/soutenir?
I'm not a native speaker but I think that supporter is more in the sense of 'to be able to cope with / to stand something'. In contrast soutenir is to support or maintain in a more positive, giving sense. This is only based on the definitions in WordReference. Having said that however I've just read that supporter can be used when talking about sports teams...