1. ´Stand in´ significa ´subtituir alguém´
Meaning: To do another person´s job at an event or work for a while, because they cannot be there; substitute someone
Ex: 1. Lisa is on leave so Amy is standing in for her at the reception.
2. My manager fell ill on the day of the presentation so I had to stand in for her.
3. (Noun) The speaker didn´t turn up so we had to find a stand-in for him.
2. ´Keep up with´ significa ´acompanhar ´
Meaning: To stay level or equal with something or someone
Ex. 1. You run too fast. I can´t keep up with you.
2. As an engineer it´s necessary for me to keep up with the latest developments in technology
3.´Call off ´ significa ´ cancelar ´
Meaning: To cancel something
Ex: 1.The meeting was called off because of an emergency.
2. She called off the wedding at the last minute.
3. They had to call off their trip due to bad weather.