20．口算．
| 50×0.46= | 0.08×125= | 0.6÷0.03= | 0.125×8÷0.125×8= |
| 0.72÷24= | 70÷1000= | 5.6÷0.56= | 7.47+5.5-7.47+4.5= |
19．如果a-b=1，那么a和b的最大公因数是（ ）
0 154439 154447 154453 154457 154463 154465 154469 154475 154477 154483 154489 154493 154495 154499 154505 154507 154513 154517 154519 154523 154525 154529 154531 154533 154534 154535 154537 154538 154539 154541 154543 154547 154549 154553 154555 154559 154565 154567 154573 154577 154579 154583 154589 154595 154597 154603 154607 154609 154615 154619 154625 154633 199269
| A． | a | B． | 1 | C． | b |