"Has been waiting" should be your answer. a simple predicate is the verb or verb phrase in the sentence and it usually tells what the subject does.
The correct answer is the last option: If you take away the suffix –n and the prefix un-, the root word is “know”.
Prefixes and suffixes are sets of letters that are added at the beginning (prefix) or end of a word (suffix). They are not words by themselves, but they do change the words' meanings or categories.
In this case, the root is know. The suffix -n is used to change the word's category from verb (know) to noun (known). While, the prefix un- is used to mean NOT. As a result the meaning of the word UNKOWN would be not known or familiar.
