What the verb "mark" mean in this sentence ? "Probably nothing marks someone struggling to learn English quite as much as improper use of English verb's person and tense" Can I understand the sentence above like this: "The improper use of English verb's person and tense is probably what make learners struggle most when learning English" I've found this work "mark" in dictionary, but in this sentence it do not make at all. I've tried to use all the possible meaning, but still can't figure out the meaning of the sentence.