Why doesn't BitLocker encrypt the BitLocker boot partition (as opposed to the OS data partition)?

Why doesn't BitLocker encrypt the BitLocker boot partition (as opposed to the OS data partition)? (Mark all that apply.)

Note: Make sure you select all of the correct options—there may be more than one!

1. Encryption would be too expensive this early in the boot process
2. The TPM measures the contents of the BitLocker partition, so adversaries would not be able to tamper with its contents
3. The BitLocker boot partition is not encrypted, but the keys stored on that partition are encrypted
4. The boot partition contains no secret information that needs to be protected from disclosure