You may like to look at the first tip about stranding, before continuing with this one.
Prepositions can also be stranded and when they are they are usually pronounced with their strong form even when unstressed. The prepositions most often affected are at for from of. Here are some examples:
1. What are you laughing at? ˈwɒt ə ju ˈlɑːfɪŋ æt
2. That’s what I was waiting for. ˈðæts wɒt aɪ wəz ˈweɪtɪŋ fɔː
3. Where did you buy it from this time? ˈweə dɪdʒu ˈbaɪ ɪt frɒm ˈðɪs taɪm
4. She’s the woman I was trying to think of. ˈʃiːz ðə ˈwʊmən aɪ wəz ˈtraɪɪŋ tə ˈθɪŋk ɒv