根据句意和汉语注释，写出单词的正确形式。
The famous person often makes some ______________ (演讲)on protecting wild animals.
He feels happy by ________ (志愿) to work for the charity.
They have no money to afford________________(医学) treatment
They are very interested in these ________(发明).
He _________(表演) so wonderfully yesterday.