Comprehension:

Read the passage carefully and choose the best answer to each question out of the four alternatives

All viruses are made up of two kinds of substance. First, all viruses contain proteins. Proteins are chemical substances that occur in all living creatures. A particle, or molecule, of a protein consists of a long chain of substances called amino acids. There are about 20 different kinds of amino acid in proteins. These can be arranged in any order on the protein chain. Different kinds of plant or animal contain proteins with different arrangements of amino acids. The protein generally forms the outer coat of a virus. This outer layer of protein encloses the second kind of substance found in all viruses-nucleic acid.