There were two fountain pens on the desk that Nat and Ozzie shared. The red pen, which was slightly longer, belonged to Nat. The pen that was green was Ozzie’s. The men had had a falling out since the Sox had won the World Series. That’s why Ozzie was delighted with the memo from management: There were to be no pens, pencils or food lying about on desks after work. Whatever was found by the cleaning staff would be confiscated.
Ozzie decided all he had to do was come back to the office at night and mess up Nat’s desk, which would infuriate management, who would then fire Nat.
At 1 a.m., Ozzie carefully entered the office building When he found Nat’s desk, Ozzie emptied everything in the pencil holder on to the floor; then he overturned Nat’s trash basket, which was holding the shards of pencils he’d sharpened
Remember: “that” starts words you need for the meaning of the word or words before “that,” and they aren’t separated by a comma; “which” starts words that aren’t crucial to the meaning of the words before it, and they are separated by commas
1) The tight rope walker always used a rope (that/,which…,) he’d used before.
2) Peppy, the poodle, never wanted the leftovers from dinner (that/,which…,) were always plentiful.