diff --git a/mini-lsm-starter/src/mem_table.rs b/mini-lsm-starter/src/mem_table.rs
index c854ad7..15e05d8 100644
--- a/mini-lsm-starter/src/mem_table.rs
+++ b/mini-lsm-starter/src/mem_table.rs
@@ -99,7 +99,7 @@ impl MemTable {
         unimplemented!()
     }
 
-    /// Implement this in week 3, day 5.
+    /// Implement this in week 3, day 5; if you want to implement this earlier, use `&[u8]` as the key type.
     pub fn put_batch(&self, _data: &[(KeySlice, &[u8])]) -> Result<()> {
         unimplemented!()
     }
diff --git a/mini-lsm-starter/src/wal.rs b/mini-lsm-starter/src/wal.rs
index 25329ae..c9172a9 100644
--- a/mini-lsm-starter/src/wal.rs
+++ b/mini-lsm-starter/src/wal.rs
@@ -15,15 +15,16 @@
 #![allow(unused_variables)] // TODO(you): remove this lint after implementing this mod
 #![allow(dead_code)] // TODO(you): remove this lint after implementing this mod
 
+use anyhow::Result;
+use bytes::Bytes;
+use crossbeam_skiplist::SkipMap;
+use parking_lot::Mutex;
 use std::fs::File;
 use std::io::BufWriter;
 use std::path::Path;
 use std::sync::Arc;
 
-use anyhow::Result;
-use bytes::Bytes;
-use crossbeam_skiplist::SkipMap;
-use parking_lot::Mutex;
+use crate::key::KeySlice;
 
 pub struct Wal {
     file: Arc<Mutex<BufWriter<File>>>,
@@ -42,8 +43,8 @@ impl Wal {
         unimplemented!()
     }
 
-    /// Implement this in week 3, day 5.
-    pub fn put_batch(&self, _data: &[(&[u8], &[u8])]) -> Result<()> {
+    /// Implement this in week 3, day 5; if you want to implement this earlier, use `&[u8]` as the key type.
+    pub fn put_batch(&self, _data: &[(KeySlice, &[u8])]) -> Result<()> {
         unimplemented!()
     }
 
diff --git a/mini-lsm/src/mem_table.rs b/mini-lsm/src/mem_table.rs
index 74b72a7..6460be9 100644
--- a/mini-lsm/src/mem_table.rs
+++ b/mini-lsm/src/mem_table.rs
@@ -121,7 +121,7 @@ impl MemTable {
         Ok(())
     }
 
-    /// Implement this in week 3, day 5.
+    /// Implement this in week 3, day 5; if you want to implement this earlier, use `&[u8]` as the key type.
     pub fn put_batch(&self, _data: &[(KeySlice, &[u8])]) -> Result<()> {
         unimplemented!()
     }
diff --git a/mini-lsm/src/wal.rs b/mini-lsm/src/wal.rs
index 2bd5812..739478e 100644
--- a/mini-lsm/src/wal.rs
+++ b/mini-lsm/src/wal.rs
@@ -23,6 +23,8 @@ use bytes::{Buf, BufMut, Bytes};
 use crossbeam_skiplist::SkipMap;
 use parking_lot::Mutex;
 
+use crate::key::KeySlice;
+
 pub struct Wal {
     file: Arc<Mutex<BufWriter<File>>>,
 }
@@ -93,8 +95,8 @@ impl Wal {
         Ok(())
     }
 
-    /// Implement this in week 3, day 5.
-    pub fn put_batch(&self, _data: &[(&[u8], &[u8])]) -> Result<()> {
+    /// Implement this in week 3, day 5; if you want to implement this earlier, use `&[u8]` as the key type.
+    pub fn put_batch(&self, _data: &[(KeySlice, &[u8])]) -> Result<()> {
         unimplemented!()
     }