英和和英

an important problem

a grave problem

serious trouble

a weighty problem

a major issue

weighty problems

a problem of minor importance

the grand question

a matter of first importance

the core of the problem

the core of the problem

a problem of the first magnitude

a matter of critical importance

a matter of great significance

an important subject

primordial matter

a major question

a heavy matter [problem]

a problem of great urgency

the guts of a problem

the most serious issue is

The most serious problem is...

a big problem

the central cause of the problem

the magnitude of a problem

an issue of capital importance

the root of the problem

an issue that becomes a problem

a formidable problem

a matter of special importance