linear algebra – Prove that there is a natural injection $U otimes V rightarrow E otimes F $

­­Hello everyone I found the following statement in my lecture :

Let $U$ a subset of $E$ and $V$ a subset of $F$ , so there is a natural injection $U otimes V rightarrow E otimes F $

But I don’t exactly see why it’s true , and what they mean with natural injection ? Any help would be a lot welcomed thanks in advance.