He gave us another piece of advice, ________ of great help to the research work. 

Lawrence Craven, a doctor from the USA, is the author of several published reports, one of ________ introduced the idea in 1953 _________ aspirin could reduce the risk of heart attacks.

Mass deaths of birds were not unheard of, but they normally happened unnoticed at sea or in rural areas away from towns. Many birds are weak and die in winter _______ food is scarce.

 When deeply lost in thought, _______ he often was, he would forget all about eating or sleeping. 

____ the teacher expected, the students were very excited after hearing the good news.