B!
assimilate : <span>(of the body or any biological system) absorb and digest (food or nutrients)</span>
The is...........................A
If I'm not mistaken, your answer would be B fam. Hope I helped.
Personal pronouns, "I, I'm, I'll I'd" etc. must be capitalised. As for the middle of a sentence, I'm contains "I" and so therefore it is capitalised.