The sentence “She lost bag last week” is grammatically incorrect because it does not contain the necessary determiner before the singular countable noun “bag.” The correct sentence is “She lost the bag last week” or “She lost a bag last week,” depending on the intended meaning. The structure of English requires attention to word order, articles, nouns, verbs, and adverbial expressions. The sentence follows the basic English pattern of Subject + Verb + Object + Adverbial. “She” is the subject, “lost” is the verb, “the bag” is the object, and “last week” is an adverbial expression of time. English generally has a relatively fixed word order, so these elements normally occur in this sequence: “She lost the bag last week.” “She” is a third-person singular personal pronoun functioning as the subject of the sentence. It refers to a female person whose identity is understood from the context. As the subject, it occurs before the main verb. The verb “lost” is the simple past form of “lose.” The use of “lost” is appropriate because “last week” clearly indicates that the action occurred in the past.