Choose the right grammatical form in each gap to complete the text

I have [sister|a sisters|a sister|sister's]. Her name is Liz. She is the best sister in the world. She always helps me to do my [homeworks|homework|a homework|a homeworks]. Today she's helped me to understand the difference between countable and uncountable [noun|a noun|a nouns|nouns]. Now I know that all [liquids|a liquids|liquid|a liquid] and abstract nouns are uncountable. There are also some uncountable words that I have to remember, e.g. love or [a money|money|moneys|a moneys].