“Each” as a subject is always singular: think of it as equivalent to “every one.” The verb whose subject it is must also be singular. Some uses, like “to keep them from fighting, each dog has been given its own bowl,” cause no problem. No one is tempted to say “have been given.” But when a prepositional phrase with a plural object intervenes between subject and verb, we are likely to be misled into saying things like “Each of the children have to memorize their own locker combinations.” The subject is “each,” not “children.” The tendency to avoid specifying gender by using “their” adds to pressure toward plurality; but the correct version of this sentence is “Each of the children has to memorize his or her own locker combination.”

The solution is in the “each”. Each is singular, it refers to the members of a group (in this case, tall buildings) one by one. Therefore, it has to be “was” (songular) rather that were (plural) and later “at the time that it was built”.

1)the empire state building

2)the sears tower

3)the canadian national tower,

individually, not all the 3 at the sametime, see the ‘each’ at the beginning of the phrase, try to say the phrase ‘each were….’

for the 2nd phrase ‘*they were*’ is also correct as there were no time frame involve,

Chek out this website for information on subject/verb agreement: http://owl.english.purdue.edu/owl/resource/599/01/

when it says each of these…. it is not grouping the buildings….they are singled out.

say it out loud with just one building at a time…

i hope this helps you

Each is ALWAYS singular, Asker.

change your each as both .