阅读下面短文，从短文后所组的A、B、C三个选项中选出能填入相应空白处的最佳选项。

nEw york, lonDon, pAris AnD othEr Big CitiEs ArE ExCiting plACEs to livE in. thErE ArE {{u}} (41) {{/u}} intErEsting things to sEE AnD to Do. you CAn go to {{u}} (42) {{/u}} kinDs oF musEums, plAys AnD Films. you CAn Also {{u}} (43) {{/u}} things From All ovEr thE worlD、 But thErE ArE sErious proBlEms in Big CitiEs, {{u}} (44) {{/u}}. it’s {{u}} (45) {{/u}} to livE thErE, AnD thErE ArE too mAny pEoplE in somE plACEs oF Big CitiEs.EvEry yEAr mAny pEoplE movE to thE CitiEs, BECAusE thEy CAn {{u}} (46) {{/u}} FinD joBs, to stuDy At gooD sChools AnD to rECEivE gooD mEDiCAl CArE thErE.But {{u}} (47) {{/u}} thEsE pEoplE CAnnot FinD work or A gooD plACE to livE in.Also too mAny pEoplE in A smAll {{u}} (48) {{/u}} mAkEs it hArD to kEEp CitiEs {{u}} (49) {{/u}} AnD ClEAn. somE pEoplE Enjoy living in Big CitiEs, othErs Do not. {{u}} (50) {{/u}} pEoplE movE to A Big City, thEy shoulD think ABout thE proBlEms oF living thErE.

A．

A、AFtEr

B．

B、sinCE

C、

C、BEForE