I believe that we use the following words in this context.
like - used to compare nouns, is a preposition.
as - used to compare verbs, is a conjunction.
than - conjunction.
Now in this sentence -
The new sports car is heavier than
usual for a performance automobile, but its exceptional because of its high-powered engine.
1-
2- is usual
3 - it is usual
OA is 2 since a verb is required here.
Salt depsoits and moisure threaten to destroy the Mohenjo-Daro excavation in Pakistan, the site of an ancient civilization that flourished at the same time
as the civilizations in the Nile delta and the river valleys of the Tigris and Euphrates.
The above sentence is grammatically correct as per the OA.
I am posting the OA now itself bcos my doubt is based on the explanations for the two sentences

.
my doubt - shouldn't the second sentence also have a verb after as like -
Salt depsoits and moisure threaten to destroy the Mohenjo-Daro excavation in Pakistan, the site of an ancient civilization that flourished at the same time as did the civilizations in the Nile delta and the river valleys of the Tigris and Euphrates.
how can we assume the verb in the second sentence when not in the first sentence since both than and as are used as conjunctions.
can anyone tell the exact usage of like,as and than.
Thanks.