What does this expression mean: Behind the times?

[Kellys]

Test No. incompl/advan-14 "Time Expressions (2)", question 4

You can tell just looking at their out of date equipment that the company is well ......... the times.

(a) behind
(b) across
(c) under
(d) outside

Test No. incompl/advan-14 "Time Expressions (2)", answer 4

You can tell just looking at their out of date equipment that the company is well behind the times.

Correct answer: (a) behind

Your answer was: incorrect
You can tell just looking at their out of date equipment that the company is well under the times.
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Hi Alan:
If you don't mind to explain to me the meaning of :"well behind the time?" in the sentence.

Thanks in advance for your help.

[Alan]

This means oldfashioned/out of date/ antiquated.
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English as a Second Language
You can read my ESL story Only Three Letters

[Lost_Soul]

Hi, Alan
Do we need "by" in that sentence, i.e.
You can tell just by looking at their out...