The combination of singular and plural in the English sounds odd to me here. I would write either "Is the second a unit of time" or "Are seconds units of time?"
Terima kasih Pak James.
Your suggestions are added to the list of acceptable answers.
Oddly enough, my brain thinks "Are seconds a unit of time" is ok, despite it obviously not agreeing on number.
Are seconds a unit of time
Duo Lingo, Please have a look
Is second a unit of time should also be correct
Cuma beda dikit AKMJ
Eh salah maksudnya asw
Typo lagi -.-