[½»Á÷] Funny English quiz in everyday£¨NO.11£©

Previously
Q: My first letter is in chocolate but not in ham, My second is in cake and also in jam, My third at tea-time is easily found, My whole is a pet who¡¯s often around.What am I?

A: cat.

Today¡¯s Question
You can see it, but you can't touch it. It may disappear, but has never really left you. It grows throughout the day. What is it?

We will hold this column everyday, the one who write the right answer first can earned 1 BB.
If u missed it this time, please come on and come here early, then use your smart head to find the answer.
I will give u the right answer in the column tomorrow.
So good luck to u!