41.   The heavy rain has been causing serious problems on the roads.

42.   The most serious problem about complete participation is a moral one rather than a practical one.

43.   The most serious problem arises when one attempts to compare surveys carried out by different organizations.

44.   The strike has caused serious problems, but we hope bus services will quickly return to normal.

45.   These are serious problems and reading this leaflet can not solve them.

46.   They encountered serious problems when two members of the expedition were injured.

47.   This state of affairs has aggravated the already serious problem of doubt among Christians.

48.   Though selection of countries lies at the heart of comparison, selection without reflection May lead to serious problems of inference.