18.已知∠1=42°45′,则∠1的余角等于( )
| A. | 47°55′ | B. | 47°15′ | C. | 48°15′ | D. | 137°55′ |
17.下列各式中是分式的是( )
0 282219 282227 282233 282237 282243 282245 282249 282255 282257 282263 282269 282273 282275 282279 282285 282287 282293 282297 282299 282303 282305 282309 282311 282313 282314 282315 282317 282318 282319 282321 282323 282327 282329 282333 282335 282339 282345 282347 282353 282357 282359 282363 282369 282375 282377 282383 282387 282389 282395 282399 282405 282413 366461
| A. | $\frac{{a}^{2}}{3}$ | B. | $\frac{x-y}{2}$ | C. | $\frac{1}{x+y}$ | D. | $\frac{2016}{π}$ |