Correct the following sentences: 13. Andrew already buy milk when I saw him yesterday. 15. Mary always fall down because she was so absent-minded.

Okay, let's correct these sentences!

Sentence 13: "Andrew already buy milk when I saw him yesterday." This sentence needs a bit of work. We need to use the past perfect tense because the buying of milk happened before you saw him. Also, "buy" needs to be in the past participle form, which is "bought." So, the correct sentence is:

Corrected Sentence 13: Andrew had already bought milk when I saw him yesterday.

Sentence 15: "Mary always fall down because she was so absent-minded." Here, we need to correct the verb "fall" to the correct tense since Mary *always* does this. We should use the simple present tense but remember to conjugate for the third person singular (Mary). So, the correct verb is "falls." The correct sentence is:

Corrected Sentence 15: Mary always falls down because she is so absent-minded.