问题 单项选择题

蚕豆植株细胞中具有大液泡的是______。

A.根尖分生细胞
B.成熟的叶肉细胞
C.成熟的导管细胞
D.成熟的筛管细胞

答案

参考答案:B

解析: 液泡是植物细胞质中的泡状结构。成熟的植物细胞中才具有中央大液泡,液泡很大,可占据整个细胞体积的90%。故A错。成熟的导管细胞只具有细胞壁。故C错。成熟的筛管细胞无细胞核、液泡膜、微丝、微管、高尔基体和核糖体,但有质膜、线粒体、质体、光面内质网和叶绿体,细胞壁周围具有胼胝质,即某些碳水化合物,所以筛管是活的。筛孔间有胞间连丝相通,这有利于有机物的运输。故D错。

选择题
单项选择题

I don’t know if there’s something in the water, but my town has exploded with tons of single people! Just last year, practically the only eligibles I knew were my divorced friend Patti, my bud Fulgencio, hubby Rick’s barfly pat Craig, and Jimmy the pizza delivery guy. But now, I find-out that my cousin Michelle is leaving her second husband, and a recent chit-chat with my building’s manager Sandy revealed that she hasn’t had a serious relationship in almost five years! Besides that, at least five suspected singletons have moved into my building since June. Five!

For an incurable romantic like me, this is heartbreaking. People are meant to have sweeties! I feel so sorry for single people. How can they bear going through life alone I know a lot of them put up. that "independent" front, or use that "I’m just waiting for the right person" defense, but they’re kidding themselves. Why would anyone turn up her nose at the prospect of a beautiful wedding, a gorgeous bridal gown, and a stunning rock on her finger She wouldn’t. Why would anyone shake a stick at a warm dinner every night, a comfortable home, and a beautiful bride It just isn’t rational. And I don’t like to be harsh, but frankly, it’s depressing to see singles out in public. When I see a girl shopping for groceries by herself, or a solitary guy reading while he waits for a bus, I can’t help but sense the hollowness that single person feels inside. I’m partially psychic, so I’m aware of other people’s inner feelings.

Well, this Valentine’s Day, I’m not going to be selfish. People like me, people in successful, lasting relationships, are duty-bound to share their romantic wisdom with the less fortunate. Granted, it’s been a while since I’ve been on the dating Scene, so my chops are a bit rusty. In fact, hubby Rick is just about the only guy I’ve ever dated (Unless you count my pick for the Sadie Hawkins dance in seventh grade, Jordy DeVoe, who ditched me after about 15 minutes. Or this Oriental kid named Thant who wrapped love notes around lunchroom cookies and slipped them into my locker in ninth grade.) But Rick and I have been married nearly 20 years, so I must be doing something right. Dry those tears, Singletons! Pull your-selves together and listen to Wifey Jean. If you follow my advice, I’ll bet you dollars to donuts that you’ll find your Prince Charming, or Princess Enchanting, in no time!

The examples of her cousin Michelle and the building’s manager are used to show()

A. many people choose divorce to solve their emotional problems

B. women are not satisfied with their marriage

C. many people are not confident in serious relationships

D. more people are becoming loveless singles