Your shoes were left by the door. I know this.
Create a complex sentence.
- Correct! Use that to link to the noun-clause that your shoes were left by the door.
- Incorrect order or wrong meaning. I know that your shoes were left by the door.
- Incorrect order. You need to start with the subject + verb, which is I know. Then follow on asking What do I know? to get the object: Answer that your shoes were left by the door - a noun phrase that forms the object of the verb know. You end up with I know that your shoes were left by the door.
- Correct! You can leave out that - the meaning is still clear.
- Incorrect. Which is incorrect here, it needs to be that. You can create a similar sentence using which of...: I know which of your shoes were left by the door but it means something different. (I know you have more shoes. You left one pair by the door. I know what they look like.)