1-._______ over 100 years since the invention of the square-bottomed paper bag.
(A) Now is
(B) Now it has
(C)There is now
(D) It is now
Answer is D why not B? We don't use 'have' when talking about the time. 'He has ten years old' is a common mistake in English.
2. The invention of the compound microscope (which allowed much higher magnification through multiple lenses)
made _____ the great strides in life
(A) it possible
(D) it was possible
Answer is C but whats wrong with option A? Make something possible is correct, but you wouldn't word it like that- you'd say 'made the great strides possible'. You wouldn't use 'it' and the phrase.
3. Gold [can combined] with silver in any proportion, but alloys with 50 [to] 60 percent silver are [the_strongest].
can combined is wrong . What should be appropriate word here? It should be 'can be combined'
4-In [its] life expectancy, [although] in most [other] things, the Sun is a[typical star].
Although is wrong. Should we use even though because of the noun phrase following it? I'd use'as in most other things' It is not a contrast, so though\although don't work.
5-The modern violin, the smallest and [versatile] instrument in the violin family, is[tuned] in fifths and produces tones [ranging] over four and a half octaves.
The adjective versatile should be in superlative form in parallel to smallest. What is the superlative form? (the) most versatile- the is optional here because it is next door to the other superlative.
6-The United States, a nation with a highly diversified economy, is a major exporter of grain, fruit, [chemical], aircraft, and cars.
Chemical should be chemicals but why not aircraft as aircrafts? Aircraft is an irregular plural; like 'sheep' it doesn't change. If you used 'planes'it would show the plural suffix
7-Magnesium has little structural strength and must be alloyed with [another] metals such as aluminum and zinc when it is to be subjected to stress.
Another should be changed into other? Definitely
8-Orchid seeds take up to eighteen months to mature before they sprout, and the young plants may need another two years [to reach] at the flowering stage.
Whats wrong with to reach?. The prepostion 'at'.. arrive at\reach\get to
9-Mitosis is the normal process [by which] a cell divides, each new cell ending up with[ a ] same number of chromosomes as the parent cell.
I figured that by which is wrong but actually the preopisition "a" should be changed. My question is why not in which is used instead of by which.
I would say 'the same number'- it's specific.