They broke open the packing cases.
Is that sentence grammatical? Is "break open" an verb phrase?

Question

Answer

That statement is perfectly correct

Answer

break open, 强行破开，砸开 的意思

Answer

'They are breaking open packing cases' is present tense, whereas 'They break open packing cases' is a general statement e.g. 'Goverment officials break open packing cases when they suspect they contain something illegal' - that's not referring to something specific but something that generally happens now.