Explanation: a direct object is a noun, or noun phrase, denoting a person or thing that is the recipient of the action of a transitive verb, for example, in the sentence "my brother ate a watermelon" the transitive verb is "ate" and the direct object (the recipient of the action) is "watermelon." In the given sentence the transitive verb is "increased" and the direct object is "difficulty" notice that it answers the question "what did he increase?"
