7. The university has launched a research center to develop new ways of ________ bacteria which have become resistant to drug treatments.
Recently I bought an ancient Chinese painting, _________ was very reasonable.
The doctor did _______ he could ________ the little child.
Miss Chen can show you around _______ mountain, because she has ______ good knowledge of it.
The athletes competed ________ each other for gold medals in the Olympic Games.
All his free time is ______ by volunteer work, but he feels it meaningful.