Question

The tundra is a harsh environment.

Only the toughest plants and animal can survive.
Joining words:
And.
Or,
But,
So

Answer 1

The tundra is harsh environment so, Only the toughest plants and animals can survive.

Step-by-step explanation

Just read them i guess and see which makes more since

Answer 2

The tundra is a harsh envioroment so only the toughest plants and animals can survive.