YOU SAID:
Their are plenty of fish in the sea
INTO JAPANESE
彼らは海にたくさんの魚がいます
BACK INTO ENGLISH
They have a lot of fish in the sea
INTO JAPANESE
彼らは海にたくさんの魚を持っています
BACK INTO ENGLISH
They have a lot of fish in the sea
You've done this before, haven't you.