Why did vaccine makers have to guess which flu strains will be active months before the flu season begins?

The bird flu like other flu is caused by a virus and this virus mutates very fast with time. Mutation is a change in the genetic make up of an organism which in this case, makes them resistant to vaccines that was effective on them not too long ago.

faulty parallelism is a construction in which two or more parts of a sentence are equivalent in meaning but not grammatically similar in form.

the correct version of this faulty parallelism in the sentence is:

the hikers knew that the hike was six miles, that it usually required the entire day, and it would not be wise to start after 10: 00 a.m.

the problem is the last sentence, the first two have a basic subject+verb+object structure.

so, to give a proper balance to the structure, or better said, to give a parallel structure, we must write a basic s+v+o structure in all three sentences:

the hikers knew that the hike was six miles, that it usually required the entire day, and it would not be wise to start after 10: 00 a.m.

sufficient and relevant

explanation: