Grammar question, please help.?

Expressions of time, money and distance usually take a singular verb:
Ten dollars is a great deal of money to a child.
Ten kilometres is too far to walk.
Six weeks is not long enough.


Expressions using the phrase "number of" depend on the meaning of the phrase:
a) They take a singular verb when referring to a single quantity:
The number of students registered in the class is 20.

b) They take plural verbs when they are used as indefinite quantifiers (see rule 1 above):
A number of students were late.

Below is a very useful link from the University of Toronto which further explains the rules and gives examples:
http://www.writing.utoronto.ca/advice/english-as-a-second-language/expressions-of-quantity

Also, consult the link for information on the following:
With fractions, percentages and indefinite quantifiers (e.g., all, few, many, much, some), the verb agrees with the preceding noun or clause...

The words majority and minority are used in a variety of ways...

Adjectives preceded by the and used as plural nouns take a plural verb...

Regarding "open the umbrella"; saying open/close the umbrella is common and not incorrect in American English, perhaps English speakers of other countries may say put up/close and furl/unfurl the umbrella.

The same goes for "open the curtain", which is common usage, you may also hear draw/pull the curtain and close/shut the curtain in both American English and English from other countries.

I'm guessing the language might be in transition on this one. Which is why you'll get lots of divided answers, since different people prefer one or the other. Personally, I think I'd use either, depending on the context. I'm pretty sure I use "is" more often, though.

The difference in when I'd use which is pretty small, but allow me to tell two brief stories to illustrate what I mean.


1.
"I realized the other day, Sarah, that it's been three years since we first met," said Stephen. "And I realized that three years are not enough. I realized that you're the one I want to be with, 'in every world of God's worlds.'" He got down on one knee. "Sarah, will you marry me?"

2.
"It's not going to be easy."
Carlos stood up. "I've been working for him three years. He trusts me. I can do this."
The agent turned away, gazing out the window. "Three years is not enough to make him trust anyone." He put on his sunglasses. "You may not like the things we'll have to do to stop him."
"After what he did..." Carlos clenched his fists. "I'll do whatever it takes."


If I read these two stories to myself, I can substitute "three years is" or "three years are" into either, and they still sound fine...but I think the first is stronger with "are" and the second works better with "is". In the first story, Stephen is emphasizing that there are multiple years, all the moments that went into those three years. In the second, the agent is talking about the "three years" as a single unit of time, and he's emphasizing how insignificant it is.

Three years is not enough is correct.
It's hard to explain why this is correct. Whenever you say something with numbers like that (Two is better than one, two hours is plenty of time, etc.) , you treat it like a singular noun and use "is" instead of "are". It's just a weird rule.

Right: Three years ARE not enough. Are: plural (e.g three years) open the umbrella: correct

Because the noun, "three years" is pluralised, the verb, "is" needs to be as well. So "three years are not enough".

The use of "open" is fine in both of those examples, but the context could change that.

Is
is correct, as is
the two opens.

I would go with the former "three yes is not enough"