Multi-word verbs are big phrasal verbs. "To be up to" is an example. You need to know the important ones for FCE.

FCE USE OF ENGLISH PART 2 PREPARATION

MULTI-WORD VERBS EXERCISE

by Bob Wilson at autoenglish.org

HOME FCE READING FCE USE Part 1 FCE USE Part 2 FCE USE Part 3 FCE USE Part 4 PHRASAL VERBS OFFICIAL SITE
BE UP TO to be someone's choice MAKE SURE to assure, double check
COME UP WITH to have an idea TAKE ADVANTAGE OF to use an opportunity
GET RID OF to eliminate, dispose of TAKE PART IN to participate in
FALL INTO THE HABIT OF to start doing something regularly    
Multi-word Verbs Exercise

Multi-word Verbs Exercise

Fill the gaps.