Vocabulary completion. Choose the correct words to complete the sentences below.
How to charge a cell phone.
First ( ______ ) the power.
Then ( ______ ) the phone.
After it's charged, ( ______ ) the phone.
When you're finished, ( ______ ) the power. 空1选项：1、turn on2、turn off空2选项：1、unplug2、plug in空3选项：1、plug in2、unplug空4选项：1、turn on2、turn off