Questions & Answers about Das Haus und der Baum sind sehr groß.
Why is the verb sind used if both Haus and Baum are singular nouns?
Even though Haus and Baum are singular on their own, together they make a plural subject. Just like in English, when you connect multiple things with und (and), they become a plural "they". Because of this, you must use the plural verb form sind (are).
If the subject is plural, why doesn't groß get a plural ending like große?
Why do we use das for house but der for tree?
This happens because German nouns have grammatical genders. Haus is a neuter noun, so it takes the neuter article das. Baum is a masculine noun, so it takes the masculine article der. There is no logical reason why a tree is masculine and a house is neuter, so you always have to memorize the article with the word!
Why are Haus and Baum capitalized in the middle of the sentence?
In German, every single noun is capitalized, no matter where it appears in the sentence. Since Haus (house) and Baum (tree) are nouns, they get capital letters. Words like und (and) or groß (big) are not nouns, so they remain in lowercase.